Hippos can’t swim or float.

The word “hippopotamus” means “river horse” in Greek, which makes sense given the amount of time — about 16 hours a day — these massive creatures spend in the water. But as it turns out, hippos can’t actually swim or even float. Their dense bones and heavy bodies cause them to sink, and their short legs and broad structure aren’t built for moving through water as easily as other aquatic mammals. 

What they can do, thanks to that density, is stand sturdily on a waterbed’s floor and walk or bounce along the ground. With their eyes and nostrils located high on their heads, they can still see and breathe while almost completely submerged.

Dolphins can recognize themselves in the mirror.

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Dolphins recognize their own reflection as early as 7 months old, showing self awareness even earlier than human babies.

Although they prefer the shallower parts of lakes, rivers, and swamps — typically around 6 feet deep — they’ve been observed in waters as deep as 40 feet, which they can propel themselves above by leaping like porpoises off the bottom. Even when they sleep, they can hold their breath for only about five minutes before an automatic reflex ensures they rise to the surface for air so they can rest without drowning.

The water isn’t just a playground for these creatures — it’s vital to their survival. Staying submerged helps keep their sensitive skin cool and hydrated under the hot African sun. It isn’t until dusk that they emerge and spend the next eight hours or so on land, grazing on grasses, before returning to their aquatic refuge when the sun reappears.

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