Puppies can play rough. Puppy play consists of chasing, pouncing, barking, growling and biting. Many pet owners mistake normal play behavior as aggression or laugh off behavior that is a warning sign for truly aggressive behavior. ... It isn't normal brain development for a puppy to do that to people or other dogs.

What are signs of aggression in puppies?

The most common aggressive puppy behaviour warning signs include snarling, growling, mounting, snapping, nipping, lip curling, lunging, dominant body language/play, challenging stance, dead-eye stare, aggressive barking, possessiveness, and persistent biting/mouthing.

At what age can you tell if a puppy is aggressive?

Most puppies are through the worst of the biting phase by about four months old. After about six months of age, some puppies begin to show signs of fear aggression. This means that they may growl or snap at strangers who approach or try to touch them.