In flight a hummingbird's heart can hit around 1,200 beats per minute and its wings blur at 50-80 beats per second. To survive the night they drop into torpor, slowing everything to a near hibernation.
Two hearts pump blood through the gills and one through the body. Copper-based hemocyanin carries their oxygen and turns the blood blue.
Sharks have patrolled the oceans for about 450 million years. The first trees appeared roughly 100 million years later — sharks predate Saturn's rings too.
Their intestines have stretchy and stiff sections that mould waste into cubes — so it stays put on rocks and logs when marking territory.
These half-millimetre "water bears" dry into a tun state and shrug off radiation, boiling heat and near absolute zero — and have been revived after a space trip.
It weighs around 180 kg and beats as slowly as twice a minute during deep dives — audible from three kilometres away.
A sloth's stomach has multiple chambers and works so slowly that a single leaf meal can take up to 30 days to digest. Their whole metabolism runs at about half the rate expected for their body size.
