Of all the animals in the world,
there are some that really stand out.
Look at you.
'That we think are special.'
We find them undeniably, almost unbearably cute.
Millions of us watch these animals online.
But behind every feature we love so much -
that big round head...
PANDA CUB SNEEZES
FROG SQUEAKS
..surprising sounds...
You are super, super cool.
CHIMPANZEE LAUGHS
..or those wide eyes -
is a secret survival strategy.
CAT PURRS
I'm Gordon Buchanan.
I've filmed our favourite animals all over the world.
Now, I want to discover
the hidden biology of these animal superstars.
Whoa.
HE CHUCKLES
Why this sweet face hides a deadly secret...
HUMMINGBIRD SNORES
..why hummingbirds snore...
HUMMINGBIRD SNORES
..and penguins waddle.
PENGUIN SHRIEKS
Behind every appealing animal
is an incredible story.
And I'm going to reveal their secrets.
If you took a poll of the top 20 animals on the planet,
I reckon these guys would be right at the top.
They are fantastic, those enormous ears, their trunks, beautiful eyes.
I just love them.
But we've all got our own favourites,
animals we find irresistibly appealing.
Hello. How you doing?
Sometimes we fall for the sounds they make.
Is that an invitation for me to tickle you?
It is, it is.
Others move in ways that delight us.
But often it's simply the way an animal looks
that makes it so compelling.
And they don't come much better looking than the iconic giant panda.
Famous as a symbol for conservation...
and for its sneeze.
PANDA CUB SNEEZES
Maybe you were one of the 200 million people
that watched this online.
PANDA CUB SNEEZES
Our monochrome love affair began in the 1970s
when China gave the first pandas to the Smithsonian Zoo.
And just last year,
their newest baby had over two million visitors,
all desperate to get a glimpse.
I've come to meet the little crowd-pleaser.
Hello, Bao Bao.
You really are the most adorable panda in the world.
Pandas really have to be one of the most recognisable animals
on the planet and arguably one of the best-loved.
They are an extraordinarily good-looking animal.
Now, pandas aren't the biggest of bears.
If you want overall size,
you have to look at brown bears or polar bears,
but look at the size of that head.
It is much bigger, much rounder than that of any other bear
and it's that beautiful big face that really
stops them looking like a predator.
Makes them look less threatening
and when you look into the face of a panda,
you don't feel any threat at all.
It's her beautiful face that makes little Bao Bao so appealing.
But why is it proportionally so much bigger
and rounder than other bear cubs?
Pandas are classed as carnivores.
They have the teeth and claws of meat-eaters
but they don't act like carnivores.
Around five million years ago,
pandas actually lost the taste for meat.
They switched to the food source that was most abundant.
A sensible choice you'd think,
except a stick of bamboo has barely any calories.
Especially compared with a hunk of red meat.
So, the panda is a carnivore that has gone vegetarian
and it has chosen one of THE toughest food sources around,
this stuff, bamboo.
They don't just eat these nice leaves,
which...
urgh, to me, pretty unappetising.
They will grind and pulverise even the thickest stems.
Oh, my goodness.
You get into this stuff, look at all those splinters.
A bear like the highly carnivorous polar bear can survive for days
and days on a single kill, but for a panda,
to get enough calories to survive just eating this,
they have to eat for, wait for this, 16 hours a day.
Breakfast, lunch and dinner is bamboo.
So to cope with the challenges of a bamboo diet,
the panda's body has had to change, adapt and evolve to deal with it.
Their stomach lining has grown thicker
to deal with all those splinters.
But it's the skull that has changed most dramatically.
Just looking at this skull, you can see that it's unlike
the skull of any other bear.
The bone itself is much denser, thicker and wider
and that allows these huge jaw muscles to attach.
This gives the panda a stronger bite force than a polar bear.
And it's this bamboo diet that has created this massive head,
a massive head that has such an extraordinary appeal for us.
The irony is, when covered with fur,
this mass of muscle and bone
looks like a teddy bear.
And Bao Bao's markings only make her more appealing.
In the wild, the eye-catching black and white
actually breaks up the panda's silhouette in the snowy forest...
..and makes the eyes look bigger,
more threatening to rivals and predators.
But the illusion has the complete opposite effect on us.
So, why have we fallen for these oversized features?
Well, bizarrely, it's all down to our own biology.
Big eyes trigger exactly the same emotional response in us
as when we see the panda's oversized head and that's really
because of the way that we respond when we see our own babies.
We're all born with these big heads and big eyes
and when we see those features,
our nurturing, caring instincts spring into action.
At the sight of Bao Bao's big baby-like head,
blood rushes to our midbrain -
part of the brain's "pleasure centre".
A flood of dopamine is released,
one of the hormones produced when we fall in love.
This chemical reaction creates emotions,
it's what makes us go all gooey.
Psychologists call it the "cute response"
and the "cute response" is so powerful, primitive and deep-rooted
that it can be triggered when we see those features in other species,
in animals.
Our love of the panda is down to our evolutionary hardwiring.
We just can't help it.
The power of the cute response
was perfectly demonstrated a few years ago...
..when a funny little creature grabbed global attention.
But I warn you,
it's not as sweet a story as it seems.
A video of a ticklish slow loris took the internet by storm.
WOMAN LAUGHS
Six million hits.
We couldn't get enough of this wide-eyed little gremlin.
For loris expert Anna Nekaris,
the overnight celebrity came as a bit of a shock.
Slow lorises are very rare in the wild and so
until about ten years ago, hardly anyone had heard of a slow loris
and then they became one of the most popular animals on the internet.
For many people, a slow loris is a quintessentially cute animal.
Its head is like a little round ball on top of a round body
and it's just got a really, sweet, innocent, cute face.
But like the panda,
it's the loris' biggest feature that makes it so appealing.
Its huge eyes.
They send our cute response into overdrive.
But it's in the wild that the true purpose of those incredible eyes
and the dark side of the sweet little loris is revealed.
Lorises are nocturnal.
In the dark, their huge pupils dilate wide.
This allows all available light to pass straight into the eye.
It gives them excellent vision even in the faintest of starlight,
which they use to stalk...
..and catch prey.
They may look really cute but when they grab their prey,
they're very vicious and the first thing they do is shred its head off,
and very proudly they lick it like a little lollipop
and eat the entire thing, all the wings, all the bones.
And their appetite isn't limited to insects.
This loris has set its sights on a roosting bird.
If that isn't enough to put you off your dinner,
they have an even more unsavoury skill.
What strikes one most if you see a slow loris
is that they have a long back with a dark stripe
and when they climb they move like a snake,
their spine moves in an S-shape, and if you try to catch one,
they hiss at you just like a snake.
They raise their arms above their head
and they form a hood above their head, like a cobra.
Because the internet cutie
is the world's only venomous primate.
Lorises secrete an oil from their elbow which,
when mixed with their saliva,
creates a deadly cocktail.
We know people who've lost half a limb, who've lost fingers,
people who've nearly died and people who have died from their bite,
so it's an animal you don't want to mess with despite the fact
it looks so appealing.
So, probably best not to tickle one then.
In the case of the slow loris,
our instinctive cute response is actually misleading us.
We see those big eyes, we imagine the loris is completely harmless,
we want to care for it, we even want to own one as a pet.
And clearly as the world's only venomous primate,
it's not the best animal to have around the house.
It's illegal to buy lorises
but the demand is so high caused by these videos
that lorises have become extinct in many of their jungle habitats.
It's a cautionary tale that cute can be a curse.
Oversized heads and big round eyes
push our biological buttons.
But the power of the cute response doesn't stop there.
I'm on my way to meet another animal favourite that proves that
almost any feature can be a trigger as long as it's big enough.
This is a fennec,
smallest member of the fox family,
weighing less than a bag of sugar.
But it's not its size
that's made the fennec famous.
Those are.
This little guy has the largest ear-to-body ratio of any carnivore.
Have a look at those ears.
They are phenomenal, completely over-sized.
Don't get me wrong, I'm a big fan of all foxes,
but those ears really are extra special.
Hello. How you doing?
And you see, as he's standing there, the ears are constantly rotating.
Twitching, just drinking up every single sound.
He's showing off his specialist skill.
And fennec foxes are incredibly sweet-looking
but they're also a very efficient hunter
and those ears are the tools of their trade.
Fennec foxes live out in the shifting sands of the Sahara.
In miles of open desert,
finding anything to eat can be difficult.
A game of hide and seek.
But fennecs have two unfair advantages.
Those huge ears act like amplifiers -
they gather all the sound
and channel it towards their inner ear.
Their hearing is so pin-sharp,
he can hear things that I can't hear and it's said that they can
hear a mouse's heartbeat underneath the sand.
Quite incredible.
OK, perhaps you might expect excellent hearing
from a set of ears that big.
But they have another, even more specialised role.
It's not unusual for the temperature to reach 50 degrees in the Sahara.
Too hot for most small mammals.
But the fennec fox is different, aren't you?
You can actually see when I hold him against the light,
you can see the blood vessels through his ear.
The skin is so thin that the heat from the blood is lost
into the air, and this cooling of the blood allows him to keep
his core temperature at a safe level.
It's what keeps him alive.
So, in fact, each ear is a radiator,
which is a critical survival tool
for this fantastic desert-dwelling animal.
Facial features are clearly a key factor in
deciding which animals we find cuter than others.
But there's one last physical attribute
that tops them all.
An animal can have the biggest eyes,
roundest face,
but if it's not furry,
then forget it.
The word "fluffy" gets over 20,000 hits on search engines every week.
The furrier the animal, the better.
Which brings me to America's west coast.
We associate fur with comfort, softness and warmth
and it's no surprise really that the animals with most fur
live in cold places, so why then am I here in California?
Well, the answer to that is
that the furriest animal on the planet lives just out there.
Whoa!
HE CHUCKLES
OK, OK, there we go.
Just in front of me, I can see the faces of what I'm after -
sea otters.
They have to be the most charming animal on the water.
I mean just look at them, see that lovely round face,
long whiskers.
That one's looking a bit slick with all the water
and there's another one that's fluffing itself up a bit.
I've got round about five million hairs on my body,
a sea otter has up to 800 million hairs on its body.
That's round about one million hairs per every square inch.
That is an astonishing amount of hair
and that's what makes sea otters the furriest animal on the planet.
There are 12 other species of otter around the world,
all with impressive fur.
OTTERS SQUEAK
But it's not nearly as dense
as their Californian cousins.
So just why is a sea otter
so furry?
Sea otters spend 95% of their lives in the water.
The ambient temperature is really quite warm
but the water itself, quite chilly, maybe round about 10 degrees.
If I fell in there, I probably wouldn't last that long.
Other sea creatures like sea lions, walruses, they've got blubber,
it's this thermal layer that protects their bodies.
Sea otters don't have the luxury of blubber,
but what they do have is fur, lots and lots of fur.
What we see are the long, tough guard hairs.
They provide a barrier but aren't completely waterproof.
Below is the otter's secret weapon.
A dense, soft underfur.
By rolling, rubbing and fluffing,
they push and trap air in between their fur fibres...
..which stops cold water ever reaching their skin.
But a sea otter's coat is more than just a dry suit.
It plays another fundamental role in their survival out at sea.
Sea otters are the most recently evolved marine mammal
and so they're not as fast as seals and sea lions
in terms of their ability to catch, you know, swimming fish.
Here in California,
they eat somewhere between 60 and 65 different species of prey items.
Typically crab, sea urchin, clam, mussel.
One of the adaptations that sea otters have for eating these
hard-shelled prey items is that they're tool users.
In some cases,
it's as simple as picking a rock up off the bottom of the ocean
and cracking clams or mussels.
But in other situations, it can be much more complex, you know,
we've seen otters that use things like bottles
as either a hammer or an anvil.
They might bang hard-shelled items against docks or boats.
Clever stuff.
But what's truly ingenious is how the fur comes in to play.
Using a tool in the middle of the ocean would be almost impossible
but all that trapped air makes the otter buoyant...
..and its stomach -
a floating work surface...
..from which they can consume up to 25% of their body weight in one day.
So, keeping this fantastically useful fur in tiptop condition
is crucial.
This pup will rely on mum to keep it warm,
dry and afloat until it learns to groom for itself.
But sometimes babies are orphaned...
or abandoned...
..and Karl and his team are called in.
At the Monterey Aquarium Sea Otter Programme,
Karl takes in pups as young as a day old.
When we get a stranded pup, all we're trying to do is basically
rehydrate the pups, start them on a bottle-feeding formula.
I should probably explain Karl's get-up.
It isn't safety gear,
this pup is about as dangerous as he looks.
The mask stops the pup thinking Karl is his mother.
If he's going to make it in the wild,
then it's best he doesn't get too attached.
To mimic the care that a pup would get from mum,
Karl and his team run an otter salon.
We start out with big broad towels
to essentially absorb most of the water.
And once the fur's sufficiently dry, we'll start incorporating brushes.
The brushes then allow us to
separate the fur and get the air flow down into the underfur.
Might take 10 or 15 minutes at a time.
That would be one grooming session and we're doing this
continuously throughout a 24-hour period with the pups.
It's a tough job, Karl, but someone's got to do it.
Their fur is so dense that they essentially float
like little corks at the surface of the water
and the water itself is not actually contacting the skin.
OTTER SQUEALS
By the time he's released back into the wild,
the pup will have learned all the skills he needs.
And his incredible fur will help him survive life
as a wild otter out in the bay.
For the panda,
loris,
fennec,
and sea otter,
supersized features are vital.
They're what allow them to live in very
different and challenging environments...
..to find food
and keep their body temperatures in check.
But appeal isn't always just about looks.
Sometimes it's the way an animal behaves
that makes it a favourite.
Elephants don't have big, forward-facing eyes,
they're not furry, they're hairy but not fluffy
and I'd argue with anyone that says this isn't cute,
so something else is going on here, something else is triggering
the cute response and I think a lot of it is to do with that nose.
Like any newborn, the first few months of an elephant's life
are a steep learning curve.
Walking is tricky enough.
But the extra appendage is even harder to get the hang of.
Elephants are born with short, stubby trunks.
But they elongate rapidly
over the first few weeks.
Mastering the movement
can be a minefield.
Baby elephants aren't born trunk-trained.
For the first few months,
an elephant's trunk has a mind all of its own
and to watch a baby elephant learn to use its trunk
has to be one of the most endearing things in nature.
So why is a trunk so hard to get to grips with?
Although we find the clumsiness endearing,
for the elephant, this period of development is fundamental
to their survival.
Because the trunk isn't just any old nose.
Elephants don't just use it to smell.
It's a straw...
..a hose...
..a snorkel...
and utensil.
While almost every other limb in the animal kingdom uses muscle
and bone together to create fine movement...
..an elephant's trunk is different.
It has no bones.
Instead muscles alone have to stretch, contract,
work with and against each other.
It's called a muscular hydrostat.
Your tongue is another example.
Tongues use eight muscles.
But, for a trunk to perform all the tasks an elephant needs,
well, it takes just a few more.
I've got just short of 650 muscles in my entire body.
An elephant in its trunk alone
has up to 40,000 different muscles
and it has to use each of those muscles in different
combinations for different tasks.
Makes learning to ride a bike look really rather easy.
Getting the muscle combination right is all about trial and error.
It takes practice to master the movement of the most complex
and useful nose on the planet.
By the time an elephant is just one year old,
it can use that trunk for drinking, lifting, pulling, twisting,
even the most precise of movements
so they're really not such slow learners after all.
The way an animal moves can be just as appealing as how it looks.
Our emotional response is amplified when it's a young animal
learning how to get this movement just right.
Clumsiness in babies of all species is another major trigger
of the cute response.
Which probably explains why we love penguins.
That wonderful waddle from side to side
makes a penguin look just like a toddling baby.
But unlike our early teetering,
a waddle isn't part of a learning process.
It isn't refined or finessed.
A chick remains Chaplin-esque
through to adulthood.
Most animals have evolved to get themselves
from A to B efficiently.
So, why do penguins resort to waddling?
Well, although they breed and bring up their chicks on land,
most of their lives are spent in the ocean.
Underwater, they are transformed.
Penguins are highly adapted to live in the water,
they have that torpedo-like shape that means
they can swim very fast and they actually really fly underwater.
Their chest muscles are very large to drive their wings.
Their legs are very short, sort of tucked away at the back.
They act as rudders.
They can reach bursts of 25mph
which, compared to, say an Olympic swimmer,
is about six maximum speed, so they're very agile.
Emperor penguins,
the largest penguins, can hold their breath for over half an hour
and can reach depths of half a kilometre,
so they're very accomplished divers and very accomplished swimmers.
Underwater, a penguin is a torpedo in a tuxedo.
But on land, these fantastic adaptations prove, well,
to be a bit of a problem.
Short legs and big feet don't help cover distance.
PENGUINS SCREECH
The waddle was written off as an evolutionary handicap.
Scientists thought that waddling was very inefficient originally
because if you look at the energy consumption of penguins
and their walking, it's very high.
It was thought that the side-to-side motion was wasted energy.
But then a study of penguin locomotion
made a surprising discovery.
By swinging their body weight over one foot,
then using momentum to pivot onto the next,
penguins barely use their leg muscles at all.
So, it looks very inefficient but it can actually
recover 80% of the energy it's using for each stride for the next one.
So, it turns out that it's the best way to get about.
If you aren't built to walk, then waddling isn't a bad solution.
Imagine this is a penguin waddling.
METRONOME CLICKS
Rather than moving forward and using energy to pick up legs and feet,
the penguin swings from side to side.
Each swing stores up energy for the next swing.
That way, a penguin can use momentum and gain ground and waddling
might not be the most elegant way of moving around but a penguin's
ability to waddle allows it to survive under the water and on land.
And penguins aren't the only animal
whose iconic movement hides a surprising secret.
Although summer days in the outback can soar past 50 degrees...
..you'll never see a hot-and-bothered-looking koala.
Scientists have recently discovered that koalas'
iconic tree-cuddling holds the key to survival in the baking heat.
While the air temperature sizzles,
the bark of a tree can be up to nine degrees cooler.
By pressing the thinner fur of their bellies against the bark,
a koala can lose some excess heat
and keep its core temperature in check.
We find weird and wonderful movements
incredibly appealing.
But for the animals,
they're perfect adaptations
to get them around a problem.
A dexterous trunk...
..a comic waddle...
or a cuddle is key to success.
But it's not just visual clues that trigger our cute response.
Sounds can be just as powerful.
This is Eli, he's a five-year-old chimpanzee
and it is incredibly easy to see why our species
has such a strong affinity for his species.
I mean, look, we could be brothers.
HE IMPERSONATES CHIMPANZEE
Well, brothers from another mother.
The mannerisms and expressions of apes
make them a firm favourite.
We are so alike.
And there's one particular behaviour,
a sound that we share,
that's recently piqued expert interest.
A troop of chimpanzees is just like any human family.
They hang out,
play and they laugh.
HE IMPERSONATES CHIMPANZEE
Eli is still a child and like any child,
he shows his enjoyment and his personality through laughter.
Are you tickly?
Are you tickly? You are.
ELI LAUGHS
If you get the right spot, he really, really enjoys it.
Look at you, look at that face.
That's good. I've got you, see?
It's really infectious, you see Eli laughing
and it makes you want to laugh.
And recently, scientists started to take laughter seriously...
..wondering whether the similarity between the sounds we make
might tell us more about our own evolution.
We were interested
whether we share our emotional
behaviours with apes
and there were some very interesting cues that indicated that
laughter may have deep biological roots.
In the name of science, Marina started tickling.
She collected footage from chimps,
orang-utans...
and gorillas.
We recorded these sounds and used these sounds in order to
conduct a systematic acoustic analysis.
When Marina gathered all the giggles together,
a pattern began to emerge.
The apes furthest away from us on the evolutionary tree,
orang-utans and gorillas,
made a very simple sound when tickled.
But tickling our closer cousins, chimps,
produced a more complex laugh sound.
Due to this matching, we could conclude that these vocalisations
that we examined were laugh vocalisations and that apes produced
laughter and that laughter is at least 13 to 16 million years old.
Bonobos, who are the most similar to us genetically,
also had the most human-like laugh.
Marina's findings show that laughter has evolved with us.
HE IMPERSONATES CHIMPANZEE
You can see when Eli laughs, he laughs like this...
ho-ho-ha-ha...
so he's using his outward breath and his inward breath.
ELI LAUGHS
You see what's happening,
when I laugh it's on the outward breath - ha, ha, ha, ha.
And that's something that we do subconsciously,
but it's because we can control our breathing
and it's our human ability to control our breathing
that has led us to develop speech,
so isn't it fantastic to think
that we might have laughter to thank for that?
HE IMPERSONATES CHIMP
You agree, it is fantastic.
'We find a chimp's laughter so appealing because we recognise it.
'It's a sound we associate with pleasure.'
ELI LAUGHS
But sometimes more unexpected sounds grab our attention.
RAIN FROG SQUEAKS
Like this desert rain frog.
Squeaking viral sensation.
RAIN FROG SQUEAKS
11 million hits and counting.
It sounds like a dog toy,
but actually this...
RAIN FROG SQUEAKS
..is the sonorous war cry of a very angry frog.
RAIN FROG SQUEAKS
Ferocious.
And there's another animal who became an internet celebrity
by making an even more surprising sound.
HUMMINGBIRD SNORES
A scientist in Peru...
HUMMINGBIRD SNORES
..captured this
escaping from the tiny body of a sleeping hummingbird.
HUMMINGBIRD SNORES
A high-pitched...
HUMMINGBIRD SNORES
..but unmistakable snore.
Hummingbirds are loved for their beauty and speed
but this one was behaving a little bit like a human.
The perfect cute response trigger.
But was the online fame deserved?
Is this bird really snoring?
Even before the snore, hummingbirds fascinated scientists.
From the day I first laid eyes on them,
they appealed to me because they are just such unique creatures.
They are the only true species of bird
that actually can hover for sustained amounts of time.
The smaller species will flap their wings about 60 times a second.
Try to move your arm that fast, it's pretty difficult.
The smallest hummingbirds weigh as little as 2g,
which is less than a paper clip.
HUMMING
This rapid movement is a lot to ask for such a tiny body.
It uses up so much energy,
that a hummingbird needs to feed almost constantly.
A sugar-rich hit of nectar every 15 minutes.
During the day, regularly sipping nectar
gives a hummingbird enough energy to survive.
But they can't do this for a full 24 hours.
They need rest.
The sun's about to set and fairly soon,
I'm going to want to go to sleep.
That's not a problem because through today, I've taken on board
more than enough calories to see me through the night,
but a hummingbird has to feed every 30 minutes or so
even when it's not flying.
To sleep through the night without feeding
could be incredibly dangerous,
so, the hummingbird is left with one drastic option
and that is to shut down entirely.
Their heart rate drops from 1,000 beats a minute to just 50.
Their breathing becomes almost non-existent...
..using just enough energy to stay alive.
It's called torpor...
and scientists like Don are only now beginning to understand it.
Most of what we know about torpor's been learned in the laboratory.
We take a hummingbird
and we will put it in what we call a metabolism chamber.
We measure the oxygen content of the air.
If their oxygen consumption gets really, really low
so that it's even difficult to measure,
then we know that the bird is in torpor.
HUMMINGBIRD SNORES
The internet footage is actually from an experiment
very similar to Don's.
The hummingbird has spent the night in torpor to save energy.
But that doesn't explain the snoring.
Sleep and torpor are very different.
When we go to sleep, our lungs are still working,
our hearts are still beating away
and we can wake up really quite quickly,
but for a hummingbird to come round from torpor,
it has to kick-start its entire body,
it has to get its breathing and its heart rate back up to speed.
Which is exactly what this hummingbird's doing.
The sound is actually a by-product of them gasping for oxygen...
..much like air rushing across a vocal chord's would.
Coming to with a snore of sorts.
The very sweet side-effect of a fascinating survival strategy.
RAIN FROG SQUEAKS
We associate high-frequency sounds with surprise, comedy...
PENGUIN SCREECHES
..and coming from such unexpected animals, they're pretty funny.
PENGUIN SCREECHES
But lower frequencies are proven to be soothing, calming -
opposite but equally powerful effects.
CAT PURRS
And it's this soothing quality that has brought us closer
to one species than any other.
CAT PURRS
This is an animal that we have an especially close relationship with.
Cats have lived side by side with us,
sharing our homes for thousands of years.
There are an estimated 200 million pet cats worldwide
and over two million internet cat videos.
I think it's fair to say we're obsessed.
They tick all the boxes.
Big forward-facing eyes,
furry,
elegant movement...
but the greatest appeal lies in the noise they make.
CAT PURRS
I'm not much of a pet cat person.
Sahara here is much more my kind of feline.
She is an eight-year-old cheetah and she is absolutely beautiful,
but she's also a very powerful predator.
So, I wouldn't quite want her sitting up on my lap
but just like a domestic cat, she also purrs.
SAHARA PURRS
Purring is a way of communicating.
It's a way of a cheetah saying, "I'm OK, I'm relaxed."
And they do it when they're grooming
and they do it when they're with their cubs.
SAHARA PURRS
Many cat species purr,
cheetah to moggy.
It's made when the muscles in the throat contract and relax...
CATS PURR
..making air vibrate past the voice box.
A purring cat is a happy cat.
But they'll also purr when injured or unwell
and this is where it gets interesting,
because purring uses energy...
..and why would a poorly cat waste precious resources?
SAHARA PURRS
Her purr really is incredible.
You can't just hear it, you can actually feel it thrumming
and vibrating through her whole body
and new research has suggested that purring
might have some hidden health benefits.
The frequency of the purr is very similar to the sound waves
that doctors use to help repair muscle and bone, so,
while she's resting, she could very well be giving her body a once-over.
Restoration.
SAHARA PURRS
But, unfortunately for us, a purr is not all positive.
Cats were first domesticated over 9,000 years ago...
..which means they've had plenty of time to get to know us.
Perhaps too much time.
Recent research discovered a second type of purr that cats use,
not to heal, but to get their own way.
It's louder and more urgent
and the masterstroke is that extra-high pitch...
CAT PURRS WITH HIGH PITCH
..a peak of 600 Hz...
..which mimics the frequency of a human baby's wail.
CAT PURRS WITH HIGH PITCH
Cats have perfected a purr that we find impossible to ignore...
..using it when they want to be fed, or to get a stroke.
It's psychological manipulation.
We are powerless to the purr.
Cunning and incredibly clever.
SAHARA PURRS
Whether it's a soothing purr...
..a massive head...
HUMMINGBIRD SNORES
..or a sweet little snore...
..the reasons we love certain animals are as diverse and different
as the animals themselves.
Every comic movement,
oversized feature,
and wonderful sound
tells a story of evolution
and survival.
Extraordinary lives need extraordinary features.
It's what makes these animals successful.
But the way that we are drawn to them,
our cute response, really is just a bizarre accident of our biology.
The way they look, the way they sound, the way they behave,
their biology, that's what's really interesting.