"Take for instance the kiss a dog gives you when you come home. It looks like love, but it could also be hunger. Wolves also lick one another's mouths, particularly when one wolf returns to the pack. They can use their sense of taste and smell to see if the returnee has caught some prey on its journey. If it did, the licking often prompts it to vomit up some of that kill for the other members of the pack to share. The kiss dogs give us probably evolved from this inspection. "If we happened to spit up whatever we just ate," says Horowitz, "I don't think our dogs would be upset at all."