“When we study play in dogs, we study ourselves.”

From a May 19 Washington Post article, "In dogs’ play, researchers see honesty and deceit, perhaps something like morality".

Take those two dogs. That yogalike pose is known as a “play bow,” and in the language of play it’s one of the most commonly used words. It’s an instigation and a clarification, a warning and an apology. Dogs often adopt this stance as an invitation to play right before they lunge at another dog; they also bow before they nip (“I’m going to bite you, but I’m just fooling around”) or after some particularly aggressive roughhousing (“Sorry I knocked you over; I didn’t mean it.”). All of this suggests that dogs have a kind of moral code — one long hidden to humans until a cognitive ethologist named Marc Bekoff began to crack it.

Play bow prodigy, Jesse: And an expert at dog play — a seasoned veteran... Zeus!