I have a 5 lb. yorkie male that plays with a 13 lb. yorkie male and he does the same thing. He postures himself with his rump first and curls around. I think it is a defensive move cause the 13 pounder is so much larger. It is so cute to watch them in action. The same one will curl his butt first right into the bigger one and then swing around and then bites him, then takes his butt position again. It is hilarious!!! He totally out maneuvers the bigger one with this butt action.
