Capybaras love water. Their feet are slightly webbed, like a duck's, so they are excellent swimmers. They eat grass on the riverbank, then slip into the water to keep cool or to hide from danger. They can hold their breath for up to five minutes underwater.
They live in big family groups - usually around ten or twenty animals, sometimes a hundred. The grown-ups take turns watching over the babies and the rest of the herd. If one capybara sees danger, it lets out a sharp barking sound, and the whole group runs for the water at once.
Capybaras are famously chilled out. Lots of other animals seem to like sitting on them - birds perch on their backs to eat insects, monkeys sometimes ride along, and yes, photographs of them resting peacefully with all sorts of other creatures are some of the internet's favourites.
Their teeth never stop growing. That is why they spend so much time chewing grass - munching helps to keep their long front teeth from getting too long. The same is true of all rodents, from tiny mice to giant capybaras.