The hippo looks like a big, clumsy beast, but they’re actually quite agile in water. They’re vegetarians, but they’re also extremely aggressive and will kill anything that disturbs their peace. Hippos float about peacefully in river bottoms until someone or something makes them feel threatened. Then they pounce – in fact, many small boats (and their passengers) have fallen victim to the hippopotamus. Hippos have even been known to wrestle and kill crocodiles who get in their way. As you can imagine, they sometimes have to stay underwater for quite some time. The hippo can hold his breath for up to thirty minutes, whereas the average human can’t last longer than two minutes.