Most YouTube videos of adorable pairs of animals from different species fail to meet scientists' definitions of "friendship" (a long-lasting bond of sacrifice, shared moments and hurt after loss). Several studies, however, have shown that animals, at least chimps, baboons, horses, hyenas, elephants, bats, and dolphins, can form lifelong friendships with individuals who are not of their species. In Kenya, there is even documented evidence of a friendship between a centenarian turtle and a young hippopotamus.