The hippo's yawn is not a sign of sleepiness or boredom but is actually a threat gesture, displaying long, thick, razor-sharp canine teeth, or tusks, with which it is capable of biting a small boat in half. Being fearlessly protective of their turf and young, hippos have killed hundreds of people in Africa - more than any other wild animal.
Hippopotamus amphibious means "river horse." The hippo, weighing 1,800 kg (4,000 pounds) and more, lives in Africa, south of the Sahara and along the length of the Nile river, although its range once included Asia and large parts of Europe.
18% of of a hippo's weight is made up by its 5 cm (2 in) skin. Interestingly, beneath the hide is a relatively thin layer of fat.
Hippos prefer rivers with deep water and nearby reed beds and grasslands, but are also found in salt-water areas near river mouths, and in lakes in Central Africa. They are hoofed vegetarians, feeding on grass, fallen fruit, and occasionally on cultivated crops such as sugar cane or corn during the night. They spend most of the day in the water.
The hippo is the third biggest land animal, slightly smaller but heavier than a white rhino (the elephant is the biggest).
In spite of its huge size - 3 meters (12 feet) in length, 1,5 meters (five feet) tall, with a mouth measuring a half meter (two feet) across - the hippopotamus can outrun a human.
The bellowing of a bull hippo measures an ear-splitting 115 decibels, sounding like the roar of a lion. (The blue whale is the loudest animal, calling out at up to 188 decibels.)
A group of hippos is called a "bloat."
