Most pet owners believe puppies tend to nip and chew on things when they are teething - losing their puppy teeth and getting adult teeth. However, this behavior is most often a form of social play.
According to VCA Animal Hospitals, social play for a puppy involves chasing an object or its owner or playing fetch. Although many owners may want to wrestle with their pup or play tug-of-war, too much time spent playing these games can send the wrong message that rough or “mouthy” behaviors are acceptable. It is too easy to get a dog worked up, making it difficult to control. These games can then lead to more problems such as biting as the pup matures.
VCA reports that puppy parents should teach their canine the degree of mouth pressure that is acceptable when playing without hurting, or breaking the skin. When pups are still with their litter mates, they will often play with a sibling and they learn quickly about “bite inhibition”. In other words, if at any point a puppy's playmate feels that the game is too rough, it will bark or yelp and then stop playing with the biting puppy. Puppies learn very quickly in this situation how much biting or mouth pressure is acceptable. Owners tend to let their puppies bite or nibble excessively on their arms and hands without giving the appropriate bite inhibition signals.
To stop this unwanted mouthiness, owners need to address the biting when it occurs. Once it starts during play, an owner should sternly say "ouch," or another key phrase such as “no biting”. An owner should then stop playing with or paying attention to the puppy to show displeasure at the poor behavior. Although this will take a few tries, once the pup realizes biting means an end to play time, it usually stops fairly quickly.