The process of anthropomorphization of an animal character usually involves a lot of implicit decisions of what should be made human-like, and what should stay the way it is. One thing is certain, though, things will not be realistic. On the other hand, some breaks from reality are less acceptable than others... Sometimes, body organs are shifted or added to funny animals, seemingly in a way to increase identification through anthropomorphism. Some other times, it's just a stylistic convention, used so the creature in question is more easily recognized than if it was drawn realistically.