cats

It's not so much that ours plays fetch, it's that she knows the toys don't move on their own. So when she feels like playing, she picks one of her many toys strewn around the house and literally brings it to us to animate it.

If it's a mouse like in this video, she expects us to throw it, and she brings it back as many times as she wants us to throw it again. If it's a string-on-a-stick toy, we're supposed to shake the thing at the end of the string and she pretends she doesn't know it's just us shaking the stick, until she gets tired.