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Two of the hearts pump blood to the gills, and the third pumps it to the rest of the body. Their blood is blue because it carries oxygen using a copper-based molecule called hemocyanin, instead of the iron-based hemoglobin that makes our blood red.

Flamingos are pink because of what they eat — tiny algae and shrimp full of natural pink-orange pigments. A baby flamingo is actually born grey and slowly turns pink over its first couple of years.

Despite having a brain about the size of a sesame seed, honeybees can learn and remember individual human faces. They use a process called 'configural processing' — looking at how features like eyes, nose, and mouth are arranged together, rather than one feature at a time.

When the weather is too dry or too cold, some snails seal themselves inside their shell with a layer of dried mucus and enter a deep resting state (called estivation or hibernation). It usually lasts weeks or months, but in extreme conditions can stretch to about three years.

Sea otters rest floating on their backs, and holding paws — called 'rafting' — keeps the group together so no one drifts away on the current. They also wrap themselves in seaweed to stay anchored in one spot.

Butterflies have taste sensors on their feet, so just by standing on a leaf or flower they can tell whether it's a good place to lay eggs or a tasty spot to drink from.

Elephants are simply too heavy, and their legs are built to support enormous weight rather than to spring off the ground. They always keep at least one foot down — but they can still run quickly and are surprisingly good swimmers.

A giraffe uses its long, grippy tongue to pull leaves from between sharp thorns. The dark bluish-purple colour is thought to work like sunscreen, protecting the tongue from sunburn while it feeds out in the sun all day.

The name comes from old stories that pictured owls as wise creatures gathering like a council. Owls can also turn their heads about 270 degrees, which helps them look around because their eyes can't move in their sockets like ours.

A shrimp's heart sits just behind its head, in the front part of its body called the thorax — so it really does look like the heart is in the head. Many of its other organs are packed in there too.

Studies show cows form close bonds with particular herd-mates and get more stressed — their heart rate rises — when they're separated from a friend. They're social animals that feel calmer together.

When rats play or are gently tickled, they make high-pitched chirps that are too high for us to hear without special equipment. Scientists link these sounds to happy feelings — a little like human laughter.

A starfish has no brain and no blood. Instead it uses a simple network of nerves and moves seawater through its body to power hundreds of tiny tube feet. Many starfish can even regrow a lost arm.

As a baby, each dolphin invents its own unique 'signature whistle', and other dolphins can copy that whistle to call it — much like using a name.

Hummingbirds beat their wings up to about 80 times every second, and their tiny hearts race to keep up. They're the only birds that can fly backwards, and they have to eat almost constantly to fuel all that energy.

A blue whale can grow to about 30 metres long and weigh as much as 30 elephants. Its heart is roughly the size of a small car, and a blue whale calf can gain around 90 kg a day just from its mother's milk.

Ants are far too small for lungs. Instead, air flows in and out through tiny holes along the sides of their bodies, called spiracles, carrying oxygen straight to where it's needed.

Gentoo penguins build their nests from stones, so a male will search for a smooth, just-right pebble and offer it to a female — a bit like giving a gift to ask, 'will you be my partner?'

That adds up to around 35 million beats a year, quietly pumping blood to every part of your body without ever taking a break. Over a whole lifetime it beats more than 2.5 billion times.

As you grow, some soft, separate baby bones slowly fuse — join together — into single, stronger bones, for example in the skull and the spine. That's why adults end up with fewer bones than babies.

The soft cushions between the bones in your spine get gently squished as you stand and sit during the day. Lying down overnight lets them puff back up, so you're about 1 cm taller when you wake.

Even though the brain is only about 2% of your body weight, it uses roughly 20% of your energy. Thinking, sensing, and controlling your whole body takes a lot of power.

Tooth enamel, the shiny outer layer, is even harder than bone. But unlike bone it can't repair itself once it's worn away — which is exactly why brushing to protect it matters so much.

Each blink spreads a thin layer of tears to clean and protect your eyes. It adds up to thousands of blinks a day, so your eyes are briefly shut for a small part of every hour without you noticing.

Smell is closely linked to memory in the brain, which is why a single scent can suddenly remind you of a place, a food, or a person from long ago.

Your arteries, veins, and tiny capillaries together stretch roughly 100,000 km. Most of them are microscopic capillaries — thinner than a hair — delivering oxygen to every cell in your body.

It's coiled up neatly inside your belly. Its job is to soak up the goodness from your food, and its walls are folded and fuzzy to give a huge surface area for absorbing nutrients.

Fingerprints form before you're even born and stay the same your whole life. Even identical twins, who share the same DNA, have completely different fingerprints.

The earliest carrots were purple, white, or yellow. Orange carrots became popular only a few hundred years ago in the Netherlands, and now they're the ones we see most often.

Chocolate starts as seeds (cocoa beans) inside the pods of the cacao tree. The beans are fermented, dried, roasted, and ground, then mixed with sugar and milk to become the chocolate we eat.

Every kernel holds a little water inside a hard shell. When it heats up, the water becomes steam and builds pressure until — pop! — the kernel bursts and turns inside out into fluffy popcorn.

Around 25% of an apple is made up of tiny air pockets, which makes it light enough to float. That's exactly why the game of 'apple bobbing' works.

Peanuts are legumes, like peas and beans, and they grow underground rather than on trees. True tree nuts include almonds, walnuts, and cashews.

That's why cucumbers taste so cool and refreshing. Being almost all water, they're very light and a nice way to help you stay hydrated on a hot day.

A pineapple plant grows slowly and makes just one pineapple at a time, taking roughly 18 to 24 months from planting to a ripe, juicy fruit.

Those little specks on a strawberry's skin are its seeds — and each one could grow into a whole new plant. Carrying seeds on the outside is one reason a strawberry isn't a true berry.

To scientists, a 'berry' is a soft fruit that grows from a single flower with its seeds inside — which fits bananas (and grapes and tomatoes). A strawberry grows differently and carries its seeds on the outside, so it isn't a true berry.

Honey has very little water and is slightly acidic, so bacteria and mould can't grow in it. Archaeologists have even found pots of 3,000-year-old honey in Egyptian tombs that were still edible.

A lightning bolt can heat the air around it to roughly 30,000°C for a split second. That sudden heat makes the air expand with a bang — the thunder we hear.

A rainbow is really a complete ring of light, but the ground hides the bottom part. From high up in an aeroplane, you can sometimes see a rainbow as a full circle.

Young sunflowers slowly turn their heads from east to west during the day to catch the most sunlight, then swing back at night. This is called heliotropism. Once fully grown, they usually settle facing east.

Certain bristlecone pine trees are more than 4,000 years old — already ancient back when the pyramids were young. They survive by growing very slowly in harsh, rocky mountain places.

Desert air is very dry and holds little heat, so nights can turn freezing. Every so often the town of Ain Sefra, on the edge of the Sahara, has actually seen real snowfall.

You can spot all three in everyday nature: ice (solid), rain or the sea (liquid), and invisible water vapour or clouds (gas). Most other substances need extreme temperatures to switch states like that.

Each snowflake grows its own six-sided pattern depending on the exact temperature and moisture it drifts through on its way down. With so many tiny differences, finding two identical ones is practically impossible.

The old saying 'lightning never strikes twice' isn't true. Tall pointy objects like the Empire State Building get struck dozens of times a year, because their height and shape attract lightning.

The Amazon is the most life-packed place on land, and new species are still being discovered there all the time. A single tree can be home to more kinds of insects than some whole countries.

Microscopic ocean plants called phytoplankton produce roughly half of the world's oxygen through photosynthesis — so the sea, not just forests, helps power every breath you take.

That's a mind-bogglingly big number — even bigger than the number of atoms we think are in the whole visible universe. The company Google was named after it, with a little spelling twist.

Romans wrote numbers using letters like I, V, X, and M, but they had no symbol for zero at all. The idea of zero as its own number reached Europe later, from Indian and Arabic mathematics.

Each fold doubles the thickness, and doubling grows unbelievably fast. After 42 folds the paper would be about 400,000 km thick. In real life, though, paper can only be folded a handful of times.

F-O-U-R has exactly four letters, matching its own value. No other English number word matches its number, which makes 'four' a fun one-of-a-kind.

It feels surprising, but you're comparing every possible pair of people, not just yourself against the others. With 23 people there are 253 possible pairs, which tips it over 50%. This is called the 'birthday paradox'.

Multiplying is like adding a number that many times. Multiplying by zero means adding it no times at all — so you're left with nothing, which is zero.

Long ago, bakers added an extra loaf to every dozen so they wouldn't get in trouble for accidentally selling bread that was a bit too small or light. Thirteen-for-twelve became known as a baker's dozen.

A googolplex is so enormous that you could never write out all its zeros. There isn't enough room in the entire universe to print them, even in the tiniest possible writing.

The Sun holds about 99.8% of all the mass in our Solar System. It's a giant ball of hot glowing gas, and its gravity is what keeps every planet circling around it.

Venus spins very slowly — one full turn (a day) takes about 243 Earth days, while one trip around the Sun (a year) takes about 225 Earth days. So a single day on Venus lasts longer than its year.

Sound travels as vibrations through air, water, or solids. Space is almost a perfect vacuum with hardly any particles, so those vibrations have nothing to travel through — and no sound can be heard.

The Moon has no wind and no rain to wear things away, so the footprints the Apollo astronauts left in the 1960s and 70s are still there — and could last for millions of years.

Jupiter is so huge that all the other planets could fit inside it together. Its famous Great Red Spot is a swirling storm bigger than the whole Earth that has been going for hundreds of years.

Saturn is made mostly of gas, so it's less dense than water — if you had a bathtub big enough, Saturn would float in it. It's also famous for its bright rings, made of countless pieces of ice and rock.

Light is the fastest thing in the universe, yet the Sun is so far away (about 150 million km) that its light still takes roughly 8 minutes and 20 seconds to reach us. We always see the Sun as it looked a few minutes ago.

Olympus Mons is about three times taller than Mount Everest — roughly 22 km high — and nearly as wide as the whole country of Italy. Mars looks red because its soil is full of rusty iron.

Astronomers estimate there are hundreds of billions of galaxies, each holding billions of stars. Added up, the number of stars is far greater than every grain of sand on every beach on Earth.

Neptune is so far from the Sun that it takes about 165 Earth years to travel around it just once. Since it was discovered in 1846, it has completed only one full orbit (finished in 2011).

The Moon drifts away from us by about 3.8 cm each year — roughly the speed your fingernails grow. Very slowly, this is also making Earth's days a little bit longer over millions of years.

A neutron star is what's left after a giant star collapses. Its material is squeezed together so tightly that just one teaspoonful would weigh about as much as a whole mountain.