Original subtitles

Let's face it, our world is downright weird.

Argh! Oh-ho!

Crawling with creatures you've never heard of.

I can't believe that's a living thing.

Full of the unexpected.

Like freak weather exploding out of the blue.

I thought I was going to die.

And rocks that spontaneously combust.

I thought it was dynamite going off.

And the unexplained.

An unborn twin discovered inside a brain?!

There were multiple hair follicles, bone and teeth.

We've scoured the globe to bring you the very weirdest stories.

Y-a-a-a-a-a-a-argh!

I could feel this intense pain,

as if you were being stabbed by hundreds of syringes.

In this series, we're going to examine the evidence,

test the science and unravel the mysteries.

We're going to discover what in the weird world is going on.

In this episode,

we'll explore some truly bizarre goings on.

How can a stroll along the beach end in catastrophic injuries?

What's causing three suns to miraculously appear in our skies?

Who is bringing gifts to a little girl?

They're my friends and some of them are, like, family.

And how can a person with perfectly good eyesight

not recognise her own children?

Now, most people love a trip to the beach in summertime.

Paddle along the shoreline, take in the fresh sea air,

maybe build a few sandcastles.

But I've got to tell you, it can be quite a dangerous place.

And I'm not just talking about forgetting your sunscreen.

I'm taking about something far more sinister.

Orange County, California.

On a beautiful summer's day in 2012,

the Hiner family headed out to take part in one of their favourite

pastimes - beachcombing.

The big prizes when you're down at the beach are sea glass.

And on that day, we'd found a piece of blue sea glass,

we'd found a piece of green.

As we would find interesting things to look at,

everyone would stop and we would, kind of,

pick whatever was our favourite rock or shell. And I would...

I was the one with shorts, so I had them in my pocket.

We're all familiar with gathering trinkets along the shore,

but Lyn's collection was about to change her life forever.

We'd been down there for probably two or three hours.

I came home, I was sitting at this counter

and I was peeling an orange

and all of a sudden, this intense heat,

this intense, er...pain was hitting my leg.

It felt like somebody had a magnifying glass outside the window

and it was aimed at my leg.

So logically, I felt like it must be a bug.

The California coast is home to all manner of dangers...

..from rip currents to sharks.

But the cause of Lyn's pain was far weirder.

Had she brought back an unexpected guest in her pocket?

Was a scorpion hiding in one of the shells?

Or a deadly cone snail, with barbs poised to paralyse?

I decide to smack my leg to kill whatever is on my leg

and what ends up happening is, I look down,

and there are flames shooting off of my shorts.

We were both, kind of, in this sort of panic of, why isn't it going out?

My husband started yelling,

"Get your shorts off, get your shorts off!"

And I'm trying to undo them with one burnt hand

and he was pulling them off. Um...

the stones were coming out of the burnt hole

and dropping on the ground

and creating small fires each place they would land.

Lyn's carefree trip to the beach cost her ten days in hospital.

All in all, she had to have six operations,

including a complex skin graft.

So, what had caused her shorts to ignite?

What had caused such terrible burns?

Even the emergency services were completely baffled.

Outside, the fire department was asking me what it could have been

and I told them all I had in that pocket were rocks.

And no-one could believe that that was what was causing it.

There was no obvious explanation.

So, the smouldering rocks found at the scene were sent for analysis.

And one, in particular, stuck in Lyn's mind.

One of the rocks actually looked like amber.

That one little rock, I thought was... What a find!

It was this beautiful, er...clear.

It had ribboning going through it.

It wasn't very big. It was very small.

But I thought, "Wow, I've found a piece of amber".

But the little orange stone wasn't amber.

Lyn had picked up something much more deadly.

There are many elements that can self-ignite.

Some, like sodium, are stable in air...

..but react violently in water.

One, however, does the complete opposite.

Phosphorous.

In water, it's stable.

But when taken out of water, it spontaneously combusts

with the oxygen present in this flask.

Burning at around 1,300 degrees Celsius.

Now, you might have encountered phosphorus before.

Perhaps in one of these, a flare, or even in matches.

It's a reactive chemical. It's certainly flammable.

But it's nothing compared to the type of phosphorus

that Lyn inadvertently picked up on the beach.

No, that was white phosphorous.

The most explosive kind.

Whilst Lyn's shorts were still damp from paddling,

the pebble of phosphorus in her pocket was stable.

But when her shorts began to dry out,

that's when the rock ignited.

So, are we talking about a new discovery in the world of geology?

A naturally-occurring, phosphorus-rich mineral?

Sadly not.

The pebble that Lyn happened upon

was most likely the explosive remnants

of an old artillery shell

left over from military exercises.

Certainly not the usual type of shell you'd expect to find on the beach.

Had the kids been the ones who carried the rocks,

a very different scenario that I would not like to even consider.

Well, what a sobering story.

Makes me think that the next time I go beachcombing

and find something a bit weird,

I probably won't put it in my pocket.

Just have an ice cream instead.

But it also reminds me of another story.

An astonishing discovery made

when someone was just out for a stroll.

Something that redefined the world of sound forever.

OK, what's the loudest animal on the planet?

ROAR!

No.

HOWL! Not quite.

TRUMPET! Nearly.

CLICK! That's it.

The blue whale.

The largest and the loudest animal on Earth.

With a call at over 188 decibels,

louder than a jet engine.

For decades, this ocean giant has held the title.

That it, until recently.

You see, scientists have discovered a new contender.

That, relative to its size, can give the blue whale

a run for its money.

So, what is this cacophonous creature?

Well, I can tell you one thing, it's a tad smaller than a blue whale.

The discovery was made by an inquisitive scientist

experimenting with a new area of research.

Some of the group were just walking along by a lake.

And they could suddenly hear a very high-pitched chirping sound,

as you'd expect to hear from an insect.

But they couldn't actually see any of the insects.

It was then it dawned on them

that there must be something actually in the water.

After much exploration of the riverbank,

James and his team discovered the unlikely source of the sound.

CHIRPING

It was the tiny water boatman.

I know what you're thinking.

What you're thinking is that that's just a little squeak.

But, at just two millimetres long,

the water boatman is producing a sound at 99.2 decibels.

That's the same as me revving up this engine!

And then, imagine if the thing was the size of a whale.

ENGINE REVS The noise would be deafening!

Unable to believe their ears, James and his colleagues

collected a few water boatmen and took them back to the lab.

You could hear them singing in the tubs.

And, of course, that then told us that these must be very loud insects

because sound doesn't transfer out of water and into air very well.

In fact, 99% of the sound in water

is lost when it transfers to the air.

So just imagine how powerful it would be out of the water.

But what's weirdest of all is how the boatmen actually produce this sound.

You see, they don't do it by rubbing their legs together.

They don't do it by rubbing their wings together.

They do it by using an altogether different part of their anatomy.

So this tiny insect makes this sound

by rubbing one part of their hard exoskeleton against another.

In essence, it's called stridulation.

So a similar thing to what grasshoppers and crickets do

to produce these rasping, er...scratchy sounds.

What really sets this story apart

is the fact that this lesser water boatman

uses part of its penis to make the sound.

That's right, you've heard it correctly.

The water boatman sings with its penis.

By rubbing the structure against a grooved section of their abdomen,

water boatmen sing, to attract females.

The fact that it's so loud is also very weird,

because the area it produces the sound with is very small.

It's about the width of a human hair.

So, water boatmen produce their massive sound

with a microscopic instrument.

Just goes to prove, size isn't everything.

Well, it's an earth-shattering serenade, that's for sure.

But from record-breaking sounds to record-breaking size.

Our next story is an assault on the senses of a very different kind.

Sumatra.

Home to some of the world's most rare and beautiful plants.

Whilst most compete to attract pollinators with delicate blooms...

..and sumptuous smells...

..one species has taken a very different path.

A bizarre turn off of the evolutionary highway.

And there just happens to be a specimen of this floral rebel

lurking in the Cambridge Botanic Gardens.

Meet the titan arum.

Reaching up to three metres in height,

this is the largest flowering structure in the world.

Blooming just once every ten years,

this is a true botanical oddity.

But it's not just its looks that are unusual.

It's also its smell.

This misfit is not interested in attracting bees or butterflies.

It aims to lure in a much more unconventional group of pollinators.

Carrion beetles -

the undertakers of the natural world.

Just as honeybees are attracted by the sweet smell of nectar,

these gruesome insects are attracted by

the scent of decomposing carcases.

Which is why this bloom smells like a corpse.

The distinctive stench is made up of a host of chemical compounds.

One of the key components is dimethyl trisulfide.

It's one of the principle ingredients in the smell of human faeces.

So, you can only imagine the stench.

Well, you can imagine it,

but a group of scientists had to get to grips with it.

Because they broke it down to analyse it

and found a ripe cocktail of ingredients.

Yes. Instead of releasing just one awful smell,

this plant releases a succession of aromas.

Beginning with rotting fruit,

then flesh and finally, rotten fish.

No. The odour is only the start of the deception.

If you imagine a plant flowering in a dense jungle environment,

it's no good being brightly coloured or easy to see

because you're in dense vegetation.

So, it's much better to attract pollinators by having a smell

which disperses over quite a big distance.

The titan arum is effectively mimicking a piece of dead animal.

It's got the colours,

if you look at the deep red, it looks like blood.

There's the yellowy textures in there.

And then with that scent, as well, of rotting flesh,

it's really doing a good job of pretending to be a dead animal.

It's a convincing con.

A plant that looks and smells like rotten meat.

But the tricks don't end there.

Using some clever chemical reactions, the titan arum

can the turn the energy it normally uses for growth, into warmth.

It's a feat that requires so much energy,

the plant can only flower very rarely.

And disturbingly, the temperature it reaches is 37-degrees C.

Human body temperature.

But, you know, it can get even hotter.

So, is this a plant pretending to be a mammal?

Surely not!

The first night it's open,

the flower heats itself up to about 40-degrees centigrade.

And that heating up allows

the chemical compounds that are made to be released.

So, for every ten degrees or so centigrade you increase temperature,

you increase tenfold the distance

that scent molecules will travel in the air.

So, by heating itself up,

it's really increasing the chances of that scent getting out

and being picked up by the pollinators.

So, the heat spreads the rancid odour further into the jungle,

to entice insects from far and wide.

It's nothing sinister.

It's a genius act of mimicry.

Lured by the smell and the promise of food,

the beetles wander around, searching for their non-existent reward.

But in doing so, they inadvertently pollinate the plant.

Exactly what it wanted.

Poor little insects. I feel quite sorry for them,

being led up the garden path.

But what a weird story this is.

A plant that generates enough heat to mimic a human body.

Whatever next?

Well, not a Day of the Triffids-style takeover, I fear.

Because, you see, the energy required to grow so big

and to produce that central heating

means that this plant can only ever flower for 48 hours.

And, in fact, the titan arum is incredibly rare,

probably because of this weird strategy.

So, not much chance of a world takeover.

From explosive rocks

to tiny insects with something to shout about

and flowers with stomach-churning fragrances.

This is only the beginning.

Right, then, what next?

Well, we're going from a remarkable story

about some surprisingly-generous garden visitors,

via the typical circuitous route,

to an unusual marine motel.

We begin our journey in Seattle.

Home to eight-year-old Gabi Mann and her family.

Like many kids, Gabi likes to collect things.

But her treasures aren't dolls or stickers.

Metal, plastic,

buttons, screws,

rocks, more glass, bones.

A lot of things.

And it's not just the content of her collection that's unusual.

It's who gave it to her.

They are my friends and some of them are, like, family.

They're really nice.

At least, most of them, I think.

Gabi's not referring to her friends at school,

but to the crows in her backyard.

Over the past two and a half years,

these generous garden visitors

have been regularly bringing her gifts.

Her collection now contains over 100 different objects -

some dropped right at her feet.

And her collection is still growing.

- Can I show you one right now? - Yeah.

I have one right in my hand.

It's a squid that I got a week ago.

The million-dollar question is,

are these birds really Gabi's friends?

I mean, could these crows really be leaving gifts specifically for her?

Now, don't get me wrong,

I'm a massive fan of the crow family, the corvids,

but I've never really seen them as

caring, sharing, gift-giving birds.

So, could this behaviour be real,

or is it just a figment of a child's vivid imagination?

I'd heard about gifting before,

but this was the most extensive collection by far I'd ever seen.

A lot of animals use gifts of one sort or the other

to convey either their status,

or their interest in another partner.

But as far as we know,

corvids are the only birds that do this with people.

Crows give gifts to people, really, to help cement a bond,

an important relationship that they have with this person.

So, how common are crow companionships like Gabi's?

There's probably 20 or 30 instances of this happening around the world.

And they all have some consistency, in terms of a person

that's been engaging quite actively with the birds.

Feeding them a lot, consistently, maybe even rescuing them.

We've had cases where a crow was stuck in a fence

and a woman took the crow out of the fence and started getting gifts.

The gifts seem to be a thank you for the food Gabi leaves out for them.

Pretty good manners.

But is there a motive behind their kindness?

Crows are undoubtedly some of the smartest animals on our planet.

They have an extremely large brain for their body size.

And because they live a long life, sometimes more than 20 years,

they can develop some cunning ways to find food.

In addition to befriending people,

studies have shown that crows are capable of using a sequence of tools

to find a tasty reward.

Something that previously, only humans and chimpanzees

were thought to have the brainpower to do.

Back in Seattle, Gabi's found that, over the years,

the gifts she's been receiving appear to have been getting more human.

So, could these super-smart crows

really be picking out gifts they know she will like?

I would not put it past these birds to make the association

between these strange objects in their environment

and humans having produced those.

It may simply be that we notice human things more also.

As humans ourselves, we don't pay attention to little bits of bark

and rock as much as we would a rubber squid.

You would notice that!

Whatever the motive, Gabi certainly has a very special bond

with the crows in her back garden.

I think I'd like a crow as a friend.

Although I did have a magpie when I was a kid.

I gave it cat food and it redistributed it

all over the bedroom, so maybe not.

But whether this is an actual case

of cross-species kindness,

or the crows swapping a few odds and ends for food,

I don't suppose we'll ever know.

Although the pragmatist in me leans towards the latter.

But there is an incredible and proven example of gift-giving

which is happening on a truly global scale.

The Amazon, one of the most biodiverse places on the planet...

boasting 10% of all the world's species...

and over 400 billion trees.

But, you know, it wouldn't be anywhere near as abundant

if it weren't for one element.

Our old friend, phosphorus.

Thankfully, not in the explosive man-made form we saw earlier,

but in its naturally occurring form, phosphate.

A vital nutrient for plant growth.

But the Amazon has a problem.

You see, every year when the rains come, they rinse through

the top layers of the soil and wash away almost all of the phosphorus.

And that's a disaster. Phosphorus is essential to life.

It's in the very DNA, a key component of the DNA in the plants.

So with no phosphorus, you've got no trunks, you've got no leaves,

you've got no parrots, sloths, jaguars.

Without the phosphorus, you've got no Amazon.

So, with the phosphorus constantly getting washed away,

how is this biodiversity hot spot still standing?

There was some mechanism that was actually replenishing that

phosphorus year-on-year.

And so, we were looking at where that phosphorus may have come from.

Potentially, it could have been

drawn in locally, on stronger winds from South America,

but actually, research has shown that it's come vast distances.

Scientists confirmed a sneaking suspicion that the Amazon

is getting a little help.

And it's in the form of a very long-distance relationship.

Because the Amazon forest...

is getting help...

from the Sahara Desert.

A barren landscape,

where temperatures can reach 57 degrees Celsius

and wind speeds top 55mph.

It's perhaps not the first place you think of helping solve

a horticultural problem on a mammoth scale.

When we think of the Saharan desert, we don't think of lush vegetation.

It's a very dry, arid area, but it's full of nutrients.

Nutrients, this place? Well, yes. It seems the Sahara also has a secret.

And that secret lies in the Bodele Depression in Chad,

a region that was once a giant lake.

Over millions of years,

aquatic animals lived,

died and decomposed in the lake,

depositing phosphorus into its sediment.

Now the lake has long since dried up,

but its dusty remains are still loaded with goodness.

And it's these particles that have been found in the Amazon.

But with 10,000 kilometres and an ocean between them,

how is the phosphorus getting there?

Well, NASA satellites have been able to shed some light.

So, the satellite data showed us

a three-dimensional structure of the atmosphere,

so we could clearly see that dust was being

taken from the Saharan desert,

from the surface of the Earth

high into the atmosphere

and then transported all the way across the Atlantic Ocean

to be deposited in the Amazon basin.

What a remarkable journey.

Although, when the dust is blown to the UK from the Sahara,

a much shorter distance,

it's often just a light sprinkling on cars and windows.

So, how much dust actually reaches the Amazon?

Every year, 182 million tonnes of dust

is lifted from central Africa.

Most of that dust falls into the ocean but about 30 million tonnes

falls into the Amazon basin

and that provides 22,000 tonnes of phosphorus

to that region every year.

And if you're wondering just how much phosphorus that is,

it's almost 2,500 truckloads.

That's quite an impressive aid package.

So, there you go.

Proof that a global love-in can actually help support

one of the world's most complex, beautiful, impressive ecosystems,

although I'm not sure the Bodele Depression gets too much out of it.

It's a bit one-sided, this relationship.

Reminds me of another one,

which could frankly be described as a real pain in the backside.

The Great Barrier Reef.

Thousands of species live here and space is tight.

It can make finding a home pretty tricky.

Even out on the quieter reef edge -

the exposed seabed offers few hiding places.

If you're neither strong or well armed, like this tiny pearlfish,

you'll need to get creative when it comes to looking for shelter.

Perhaps set your sights slightly stranger.

Enter the sea cucumber. Known as the vacuum cleaners of the sea,

they move along the sea bed, sucking in sand at one end

and then expelling it out of the other.

And it's this bizarre creature that has the solution

to the pearlfish's accommodation problem.

To find out more, we need a marine biologist.

Pearlfish, they're little fish.

They're quite vulnerable,

simply because coral reefs are full of hungry predators.

You mostly would only see them

out and about at night-time,

where they go out hunting for plankton,

the little creatures that live in the water column,

and then, during the day, they need to find somewhere to hide.

Well, all of that sounds fairly sensible

but where does the sea cucumber come in?

So, sea cucumbers have, basically, a hole at the front end

and the back end.

The front end is where the food goes in

and all sorts of things happen at that back end.

It's where they breathe, it's where they will excrete the sand

that they've been eating, any other

digestive material will come out

and that's also where they reproduce,

so it's a, kind of, one hole does many things.

And therein lies the clue.

Because the pearlfish makes its cosy home

inside the sea cucumber's bottom.

It has to be one of nature's weirdest living arrangements.

But is this honestly the best real estate available to the pearlfish?

Well, if you can imagine those sandy areas next to a coral reef,

there's really nowhere to hide. It's just flat sand.

There aren't many rocks or any other holes or crevices to hide them.

But there are sea cucumbers.

Maybe. But whilst the pearlfish

may have set its sights on a potential home,

entry isn't always guaranteed.

If a sea cucumber does have an idea there is a pearlfish around

it might close up its bottom,

so for a little while, it won't be open for guests.

If I knew there was a pearlfish around, I'd close my bottom, too.

But the resourceful fish has a solution to this problem.

By sticking the tip of its tail into the sea cucumber's rear end...

..the pearlfish cuts off its oxygen supply,

knowing that the sea cucumber will have to open up

to breathe eventually and when it does, it's home sweet home.

Pearlfish really have to be the worst tenants.

But what's really weird, although, let's face it,

what isn't weird about this story, is that the sea cucumber

could evict the pearlfish if they really wanted to.

If other fish come up and disturb a sea cucumber,

it has a really great defence mechanism.

What they'll do as a defence

is spew their guts out through their bottoms.

And this is to, basically, distract a predator that's coming along

and then they can make their slow getaway.

But this doesn't happen with the pearlfish.

Somehow, they don't trigger this fear response in the sea cucumber.

So, despite being armed with a gutsy defence, the hospitable

sea cucumber lets the pearlfish stay, which isn't understood yet.

But then, there's just no accounting for some behaviour.

Crows that bring gifts, deserts that feed forests

and sea cucumbers that put up with the very raw end of the deal.

Nature, it seems, is most unremittingly generous.

But sometimes, it's not accommodation or sustenance that it provides,

it provides something altogether different.

Inspiration.

Our next story takes us to a very frozen Heathrow Airport.

- NEWSREADER: - The drop in temperature has led to grounded planes being

frozen into their parking stands,

with the de-icer having little effect.

Despite one runway being clear,

there have been less than 10% of flights at Heathrow

over the weekend, leaving 350,000 passengers stranded.

Ice on grounded planes might cause misery

for passengers heading off to sunnier climes,

but ice forming mid-flight can be deadly.

It's caused over 600 aviation accidents

and more than 800 deaths in the United States alone.

The danger occurs when ice forms on the wing, distorting

its precise aerodynamic shape and causing the aircraft to lose lift.

It's something that has troubled aviation engineers for years.

The problem is that ice comes in many different forms.

You can imagine freezing rain, snow, sleet, freezing fog or frost.

What we wanted to make

is a paint

or surface for the airplane

that releases antifreeze when it's exposed to ice.

The current solution to ice build-up is for planes to take

a shower in antifreeze before flight.

The wings also have a highly water-repellent surface.

But there is a problem.

When the wings get really cold, the non-stick surfaces simply don't work.

Imagine this strip of cardboard is an aeroplane wing.

And just like the wing, it's been treated with a hydrophobic coating

so the water just runs off.

But as the surface temperature drops -

we've used liquid nitrogen for the same effect -

the water droplets act very differently.

They stick and clump together

and the geometry of the wing is radically changed.

And this will affect its ability to generate lift.

So, what else can be done to prevent this build-up?

This is where Konrad comes in.

In the past 20 or 30 years,

people started looking at nature,

to try to find inspiration for current technological problems.

And he found his inspiration in a very unexpected place.

My wife and I were on holiday in Panama.

And we went on a jungle tour.

As we were going to the jungle, the guide lifted up

a leaf on a palm tree and there was a little poison dart frog.

So I was very excited, started coming up close

and tried to take a picture and he said, "No, don't come up.

"These things are really dangerous."

So at that point, I was very interested. Why are they dangerous?

The reason is that their skin is covered in a potent neurotoxin.

But it wasn't the poison that Konrad was interested in.

It was how the frogs release it that sparked his imagination.

They have little glands in their skin and when they're very scared,

when they see a predator or a tourist,

they start releasing or secreting this toxin from the inner part

of the body onto the outside of the skin.

We made a surface that mimicked the structure of the frog,

that releases, in this case, an antifreeze, instead of a toxin.

Thanks to the amphibians, Konrad and his team are developing

a porous surface that mimics the frog's skin

and releases antifreeze on demand.

Who'd have thought that deadly frogs might one day save lives?

It just goes to prove inspiration can be found in the weirdest places.

The natural world can be surprisingly charitable.

Crows showing their appreciation with presents,

a barren desert providing a nutrient lifeline to a bountiful jungle

and, of course, a marine animal offering shelter to the homeless.

And finally, our walk on the weird side is going to take us

from strange lights in the sky,

to blind people with perfectly good vision,

via a drunken octopus in a toilet.

And it all starts in Florida.

911 - what's your emergency?

Despite the caller's distress, she wasn't witnessing a UFO.

What that caller was seeing was a sun halo.

So, what's producing these extraordinary light shows?

Well, it's actually something remarkably ordinary.

The haloes are made by tiny ice crystals

floating high up in the atmosphere,

like this hexagonal crystal here.

And when the sunlight passes through them,

it refracts, or bends, to a very precise angle - 22 degrees -

and it's this that produces these astonishing halos.

It takes millions of these microscopic crystals

randomly floating high in the cirrus clouds,

each scattering the sun's rays

and creating these perfect rings of light.

But if you think that's strange,

things are only going to get more bizarre.

The Alps.

Clear, cold, beautiful.

For skiers making their way on to the slopes,

their morning was about to take a turn for the weird.

Because what was about to emerge from behind the peaks

was far from a normal sunrise.

It was a thrilling spectacle for all of those who witnessed it.

This is no trick of the lens.

Either side of the rising sun where two smaller

but unmistakable mirror suns.

And this isn't the only footage of such a spectacle.

Strange sunrises and sunsets have been popping up all over the world.

Now, the footage of these triple suns is absolutely startling stuff.

But don't worry,

our solar system is not morphing into a set from Star Wars.

You might also be forgiven for thinking

that it could be camera flare,

cheap lenses or the like, but I can tell you that it's not.

But whilst ice crystals are causing sun halos,

what causes a triple sun...

..a spectacle inexplicably known as a sun dog?

Now, to get to the bottom of its formation,

we need someone who is well acquainted with the sky.

Being a professional astronomer,

you end up with is this ingrained habit, where you are just

keeping that weather eye in the sky -

is it going to be cloudy tonight? How you going to be observing?

And just noticing many of these phenomena.

A sun halo is formed from the same ice crystals as sun dogs,

but the difference is the orientation.

Sun halos, you need just random orientations

and all kinds of hexagonal ice crystals.

But to get sun dogs,

you need those ice crystals to be the flat tile-like ones

that are all perfectly aligned, perhaps by currents that are shaping

the clouds or the way that they are just drifting down in the sky.

Because it's all on a level, you get two little rainbow patches.

The sunlight is focused into areas the same distance out

as the halo, but on a level with the sun.

And it's much brighter and the colours are much more evident

because you've got much more sunlight

concentrated into those areas.

So, ice crystals are creating these spellbinding light shows, too.

There is every chance you could have seen one...

but never looked up to glimpse it.

Just think of what you're missing.

So, it's tiny ice crystals floating high up there in the atmosphere

which produce these beautiful illusions of halos and triple suns.

They really are very impressive.

But, you know, when it comes to visual illusions,

nothing at all can compete with the power of own minds.

It's a slightly embarrassing story.

It was in a bathroom stall in a public place.

There was a little coat rack

with the two little arms coming off of the coat rack.

And underneath, it was written in magic marker,

"drunk octopus wants to fight you."

Once I looked up

why I would recognise

that that was an octopus and why that person expected that I would

recognise it as an octopus is how I ended up interested in the topic.

Laura is not alone in her octopus encounter.

And it's not just coat hooks.

We live our lives surrounded by expressions,

although some faces do seem to turn up more than others.

And in the most unexpected places.

In 1994, the Virgin Mary materialised in a grilled cheese sandwich.

The edible effigy was eventually sold by its maker, Diane Duyser,

for a whopping £14,000. That's one very expensive snack.

But to this religious revelation was by no means a one-off.

Jesus has appeared in a baking tray,

a tortilla,

and even the lid of a Marmite jar.

It's not just deities in foodstuffs. We see faces everywhere.

Even everyday objects sometimes seem to have an expression.

And this phenomenon, finding faces in objects and places,

even has a name. It's called pareidolia.

And it's an area of serious scientific investigation.

You can probably see the faces in this series of objects.

But of course, we don't actually believe they are genuine faces.

That's because of a region of the brain called the fusiform gyrus.

It's working slightly differently in each side of your brain.

The left side is suggesting that this object could be a face.

But the right side is making the final decision.

And in this case, no. It's just a plug socket.

So, why is our first instinct to see a collection of shapes as a face?

The reason that we try to take something

and make it into something meaningful has to do with

survival in the very earliest stages of evolution.

Let's assume that you are out in the woods hunting and you hear

something or you see something out of the corner of your eye.

If there is not something there and you assume that there is,

you'll react to it, but there's no harm done,

if there wasn't actually something there.

So, conjuring up faces, real or otherwise,

is about avoiding predators and staying alive.

But that doesn't explain why we see so many messiahs.

Our brain is always interpreting

the information that we get from the world

to be things that it recognises and can make sense of.

The things that we're most familiar with

or that we're expecting to see, like religion, like sex,

will be the sort of things that we tend to notice more often.

Well, that explains that cheesy conundrum.

But exactly how long does it take us to develop

this remarkable ability to recognise faces?

A study at Stanford University

produced some very surprising results.

Babies. Cute? Well, sometimes.

Clever? Well, perhaps not straightaway.

You see, when it comes to making out the world around them,

babies struggle to focus, identify colours,

and even see beyond 30 centimetres during the first few months.

So, all things considered, you might not expect these little brains

to be very good when it comes to picking out a face.

Faces are critical for all of us, but especially for babies.

Faces are important

for understanding emotion,

being able to recognise different forms of expression,

when your mom is happy, maybe when your mom is mad, comes from a face.

Faraz's research has been looking into how soon

babies can recognise a face.

Using this harmless cap of sensors,

she can monitor the electrical impulses in baby Ava's brain...

to see how she responds to pictures of faces

compared to inanimate objects.

What do you see?

What is that?

The team compared the babies' responses

to the same set of tests run on adults.

We recognise faces through a process beginning with the basic

contrast of the face, the lines of the face and we piece

the information together, until we arrive at the temporal lobe.

And the temporal lobe of the brain actually has specific cells

that respond to faces.

Given the immaturity of the babies' brains, the team weren't

expecting them to be capable of complex adult-level processing.

But their results proved very surprising.

What we found was really interesting.

Infants responded to faces the same way that adults respond to faces.

The area of the brain that lit up

when we show them the faces were very similar.

It was in the temporal region of the brain that we know processes faces.

So, if babies have a maturity beyond their years

when it comes to facial recognition, has science got it wrong

all this time?

Are infants, in fact, very good at making out the world around them?

Well, no. Unfortunately not.

You see, when it comes to making out objects,

babies still have an underdeveloped response.

It's only the region responsible for making out faces which is advanced.

Faces are such an important part of our lives that we have become

tuned to seeing them in the world around us.

Most of us have no trouble, at all,

picking out a familiar face in the crowd.

In fact, you could say that facial recognition is perhaps our one

and only true human superpower.

You see, during our lifetime,

we have the staggering ability to remember

no less than 10,000 different faces.

It's remarkable, but it also begs the question, what happens

when the facial recognition areas of our brain don't work properly?

The answer can be found in Vermont.

I just thought I was bad at remembering people.

Sometimes, I can't tell who is in the picture.

If there is just one of them, I have to ask Scott, "Which one is this?"

If they're not wearing a piece of clothing that helps me

or something else.

Meet Karen Macaller.

It's funny that we have so many pictures of them,

since I can't tell them apart.

She struggles to recognise her own children -

Max and Emmy.

Now, you might be thinking that Karen is short-sighted.

When I am looking at sets of pictures,

I can really be looking very carefully at everybody's nose

and trying to find, like, the nose that's most like

that person's nose.

And I can see all the noses and I can see some are wider

and all those things.

Despite her keen observation, Karen isn't obsessed with noses.

She is, in fact, face blind.

So, it's not like there's a big blurry patch where your face is.

I can see your face.

I can see that you have a nose and eyebrows and all those things

but then, if I look at another person,

I can see they also have a nose and eyebrows

but they don't all come together to mean something,

to look like someone.

Wondering what faces look like to Karen?

Well, try identifying these two images.

You can see the facial features of each, but it's not easy

to piece them together, to actually recognise the faces.

Until you turn them the right way up.

Curiously, Karen only discovered that she was face blind

relatively recently.

I had not realised that other people perceive faces differently.

It was maybe, like, three years ago.

There was something on TV - they showed some examples of,

like, "people who are face blind can't tell these two people apart."

And I was looking at them

and saying "that's the same person" and my husband, who is watching

with me, was saying "No, that's not even close to being

"the same person."

It was an image like this one that highlighted Karen's condition.

Most of us can see that, whilst the two images are similar,

they are, of course, different people.

For those with face blindness,

it proves almost impossible to distinguish between the two.

The condition is known medically as prosopagnosia,

and a surprising number of people are affected.

Although most, like Karen, never even know they have it.

Often what happens is, they have an incident that really

slaps them in the face, so to speak, showing them that

their face recognition is really different from somebody else's.

Prosopagnosics have told me things like they would, say,

watch a movie where there's a line-up and the eyewitness is

supposed to pick out the person who committed the crime.

And the prosopagnosic says, "That's absurd. Nobody could do that.

"You'd have to have superpowers to do that sort of thing."

The best estimate out there suggest that maybe 2% of the population,

so one out of 50 people, has really significant difficulties

with face recognition.

There are some people out there who, I'm sure, never realise

that they have really significant face recognition problems.

Just imagine a life where you couldn't instantly recognise

actors in the latest blockbuster,

your work colleagues or even members of your own family.

And you didn't realise that life could be any different.

It's one of those tectonic shifts in your brain,

where you think, like, "I understand how I work

"and I understand how the world works"

and then you find out something new

and it's very different than how you thought it was.

From ice crystals with the power to create hysteria,

survival by seeing faces in sandwiches...

and not seeing faces at all,

in a weird world,

what seems an illusion can often be explained by cold, hard facts.

What a world of weirdery we live in! And do you know?

It's only going to get weirder.

Next time...

What caused a glacier to flow blood-red?

I've never seen anything like it before.

And why did frogs start growing too many limbs?

What could possibly create this weird work of art?

And what is lurking in this South American mud?

If that didn't exist and as I said it could exist,

you would never believe me, right?