"Picasso, as he so often did, said it best: An artist must be two people – one who knows how to paint, one who knows when to stop. We all know the old anti-abstraction anecdote about the chimpanzee who, given paper and colors, does a creditable “painting” which is subsequently entered into the local art show and wins a prize. What is less well known, is that left alone, the chimp will continue to apply color to the paper until he gets restless, then will roll the paper into a ball and eat it. What of those chimpanzee paintings the popular press loves so often? Ah, they were snatched away from the chimp by a curator at the moment he or she thought they were most ripe and ready. Who then is the artist?"
above written by Henry Geldsahler, from The Business of Art (edited by Lee Caplin)
In defense of animals I do think that they are capable of creative efforts that are beautiful and I have seen my share of bad abstract art done by people. Still, point taken we do need to know when to stop. Humans, like chimps can be guilty of overworking a piece. Yes roll it into a ball (um don't eat it) and don't enter it into a show! :-)