At first glance, hippos appear to be gentle, slow animals. Aside from elephants, the only ones to surpass them in size, they are Africa's largest animals. However, they are also firm and fast, which, combined with their size, makes them one of Africa's most dangerous animals. Although they spend most of their time in the water, and their closest relatives are whales, they are poor swimmers but not bad runners on land. Unfortunately, these animals are becoming increasingly scarce, and the species has been placed on a list of vulnerable mammals.