Several freshwater turtle species absorb oxygen from water pumped through the cloaca, which lets them stay underwater for long periods, especially in winter.

In shrimp, the heart sits in the cephalothorax — the fused head-and-chest section — along with most other vital organs.

Starfish (sea stars) have a nerve ring instead of a brain and pump seawater through a water vascular system instead of blood. Many can regrow lost arms.

Research on cattle vocalisations shows individual cows have distinct voices that herd mates recognise. Calves and mothers can identify each other by call.

In very dry conditions some snails seal themselves in their shells and become dormant for long periods — a state called aestivation — until moisture returns.

Laid end to end, all the arteries, veins and capillaries would stretch an estimated tens of thousands of miles — often quoted as enough to circle the Earth more than twice. Most of that length is tiny capillaries.

Nails grow a few millimetres a month, and studies suggest they grow faster on the hand you use more, in summer, and when you are younger.

The brain predicts the sensation of your own movements and dampens the response. Because there is no surprise, the tickle reflex does not fire the way it does when someone else touches you.

The masseter, which closes the jaw, can generate very high force relative to its size, which is why human bite force is surprisingly strong. “Strongest muscle” depends on how you measure — the heart and the glutes have other claims.

A newborn has around 270–300 bones and cartilage parts. Many fuse together during growth — in the skull, spine and pelvis — leaving about 206 in an adult.

Humans have about 400 types of smell receptors, and combinations of them let us tell apart a vast range of odours. Smell is also closely linked to memory, which is why a scent can bring back a moment instantly.

During the day the discs between the vertebrae are compressed by gravity, so you can lose about a centimetre of height. Lying down at night lets them recover.

The cells lining the stomach are exposed to strong acid, so the body constantly replaces them. The protective mucus layer and fast cell turnover stop the stomach from digesting itself.

The Sun is about 150 million km away and light travels at about 300,000 km per second, so we always see the Sun as it was roughly eight minutes and twenty seconds ago.

Saturn’s average density is lower than that of water, because it is mostly hydrogen and helium. It is the only planet in the Solar System less dense than water — though you would need a very large bathtub.

Sound needs a medium such as air to travel. Space has so few particles that sound waves cannot travel between them in a way your ears could detect, so an explosion next to you in space would be silent.

The giant volcano rises roughly 22 km above the surrounding plains and is about as wide as France. Its slopes are so gentle that someone standing on it might not realise they were on a mountain.

All the planets, moons, asteroids and comets together are a tiny fraction; Jupiter holds most of what is left. The Sun is so massive that it could hold about 1.3 million Earths by volume.

The Moon has no wind or rain to erase them. Unless a meteorite hits the spot, the Apollo astronauts’ boot prints could survive for a very long time.

On the exoplanet HD 189733 b, astronomers think silicate particles form clouds, and winds of several thousand kilometres per hour could blow molten glass droplets sideways. Its deep blue colour comes from those clouds.

Neutron stars are the collapsed cores of massive stars: more mass than our Sun squeezed into a ball about 20 km across. Their matter is so dense that a teaspoon would weigh roughly as much as a mountain.

Japanese researchers using ultra-sensitive cameras in 2009 found that the body emits extremely weak visible light that rises and falls during the day. It is about a thousand times too faint for our eyes to see.

Bananas contain potassium, and a small fraction of natural potassium is the radioactive isotope potassium-40. The dose is tiny — the “banana equivalent dose” is used jokingly to explain how small everyday radiation exposures are.

Both are pure carbon. In diamond each atom is locked to four neighbours in a rigid 3-D lattice; in graphite the atoms form flat sheets that slide over each other — which is why graphite leaves marks on paper.

In air at room temperature sound moves at roughly 343 m/s; in water it is about 1,480 m/s, because water molecules are packed more closely and pass vibrations along more efficiently.

Most substances shrink when they solidify, but water molecules lock into an open hexagonal crystal as ice. That is why ice floats, pipes burst in winter and lakes freeze from the top down, protecting the life below.

Measurements of a blue whale heart preserved in Canada put it at around 180 kg. Blue whales are the largest animals known to have ever lived, up to about 30 m long.

Their diet of eucalyptus leaves is low in nutrients and hard to digest, so koalas save energy by sleeping or resting for most of the day.

In University of Washington experiments, researchers wearing a particular mask captured and released crows. Years later, crows in the area still scolded anyone wearing that mask — including birds that were never caught.

A forager returning to the hive performs a “waggle dance”: the angle of the dance shows the direction of the food relative to the Sun, and the length of the waggle shows the distance. Karl von Frisch shared the 1973 Nobel Prize for decoding it.