Beavers and their dams play an important role in nature. Because of the dramatic effects their dams have on surrounding ecosystems, these mammals are considered a keystone species. By constructing dams they create wetlands -- lush environments which attract fish, ducks, frogs and other creatures. However, beavers can become a big headache for farmers and landowners -- a problem we'll examine later in this article.
The third largest land animal, the hippopotamus is one of the most dangerous is aggressive mammals on Earth. Test your knowledge of these hulking beasts with the hippopotamus quiz.
If you're wandering through a thrift store and happen upon a large mass of some sort of waxy substance, take a closer look. It could be the rare "floating gold" of the sea: whale vomit. Find out whether cetacean upchuck can help you retire.