E.G.

As far as I can tell, IMDB classifies both humans and animals as "actors."  For instance, apparently a dog named Rocky played a character with the name "Scrooge the Dog, a.k.a. Crazy Wheels" in a movie called The Dirt Bike Kid. 

I think there should be a separate category for animal "actors."  For one thing, animals don’t seem capable of imitation — at least, not intentional imitation — and therefore don’t "act" in the relevant sense.