Puppies can play rough.
Most puppy play consists of chasing, pouncing, barking, growling, snapping, and biting. So how can you tell the difference between normal play and possible signs of aggression in both dogs & cats?
In normal play, a puppy may play bow (lower its head and raise its hind end), present its front end or side to the owner, hold the front part of its body up, wag its tail, dart back & forth, emit high-pitched barks and growls, and spontaneously attack. Of course, even normal play can become too intense.