[Bugs Bunny]? is the archetypal furry. He clearly isn't a rabbit; he walks on two legs and has hands. Yet he clearly isn't a human. He's yerf. Another example is the race of humanoid ducks found in the role-playing game RuneQuest.
There is a lot of yerf to be found on the Internet, primarily drawn by amateur artists.
Mature, adult, or pornographic yerf is also known as yiff or spooge.