You might yawn when you are sleepy or bored, but when a hippo yawns—look out! With that big yawn, it shows its very long canine teeth, warning other hippos it’s not happy. Adult male hippos often fight over control of hippo herds, and their sharp teeth make dangerous and sometimes deadly weapons.

Something as big and strong as the hippo must need a lot to eat, right? Actually, the hippo’s diet consists of grasses it finds in and near water. The 100 pounds of grass it eats a day isn’t too much when you consider a hippo can weigh nearly 100 times that much. Hippos don’t need to eat many calories because they spend most of their day snoozing in the water to keep cool, which doesn’t take much energy. Because a hippo’s eyes, ears, and nostrils all sit on top of its head, it can keep nearly all of its body underwater and out of the sun. Hippos are excellent swimmers and have the ability to walk along the bottom of lakes and rivers. They can close their ears and noses and stay underwater for up to five or six minutes.

At night, hippos leave the water and graze nearby for several hours. Their wide lips make a perfect lawnmower! This has gotten them into trouble with humans, however, who have killed hippos because they have eaten or trampled crops. Hippos are also hunted for their meat, fat, and hide, and there is a concern they are being hunted for their teeth, which can be carved just like the ivory tusks of elephants. The hippo is not endangered, but it is vulnerable if this kind of hunting continues.