Do rats feel joy? It can be hard to tell, since they can’t exactly greet us with a grin. But now, for the first time, scientists have spotted the rat equivalent of a smile—and it’s all in the ears.

Word to the wise: Don't play poker with your dog. He can read your face like a book. A new study shows that man's best friend is remarkably good at discerning happy expressions from angry ones — even ...