It makes a certain kind of barnyard sense that the occasional goat might enjoy hanging with a horse. But tigers and bears, despite what "The Wizard of Oz" might lead you to believe, would only canoodle in captivity. As Arizona State University psychology professor Clive Wynne told the New York Times, many interspecies relationships documented on YouTube and the like occur in human-controlled environments, closer to a cultivated garden than a patch of wildflowers.
Dogs, domesticated by humans, are particularly known to adopt other animals - either instinctively or empathetically, National Geographic points out. And there's no denying that dogs playing with other critters look pretty darn cute, too.