Animals
A narwhal's tusk is actually a tooth
The spiral tusk is an overgrown left canine that erupts through the lip and can reach three metres. It is packed with millions of nerve endings, making it a giant sensory organ.
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Octopuses have three hearts and blue blood
Two hearts pump blood through the gills and one through the body. Copper-based hemocyanin carries their oxygen and turns the blood blue.
Sharks are older than trees
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.
Wombats produce cube-shaped droppings
Their intestines have stretchy and stiff sections that mould waste into cubes — so it stays put on rocks and logs when marking territory.
Tardigrades can survive the vacuum of space
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.
A blue whale's heart is the size of a small car
It weighs around 180 kg and beats as slowly as twice a minute during deep dives — audible from three kilometres away.
Sloths take a month to digest one meal
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.