When Vladimir Dinets first heard several years ago that a Cuban crocodile at Ohio's Toledo Zoo appeared to be playing with an inflatable ball, he didn't think anything of it—at first.

Zookeepers reported that the reptile attacked the ball and then blew bubbles in the water, which are textbook examples of play.

But when he looked through the research literature on crocodiles and play, he found nothing on the subject. (Read more about American crocodiles.)

"People who worked with crocodiles didn't think of publishing anything because they thought [the idea of crocodiles playing] was too obvious," said Dinets, a biologist at the University of Tennessee at Knoxville.

He set out to fix that problem. In a new study in