Mouthiness in puppies, however undesirable, is a normal, natural behavior. The sense of taste and touch in and around the mouth are some of the first senses to develop. Hence, puppies use their mouths to gather information about their environment. When a whelping mom has the chance to raise her puppies to adulthood, she teaches them about biting – what is "too hard" and what constitutes "too much". Since most of us acquire our pups without their mother’s having had a chance to teach them these rules, it is our responsibility to help them learn how 'not' to use their mouths. Some use of the mouth for exploration is acceptable in puppies less than 4 months of age; however, biting that is repetitive or in the least bit painful should be discouraged. Here are some tips for discouraging mouthy behavior

1. Avoid rough or aggressive play, especially interactions which involved a puppy's mouth and your hands or feet. The more aroused and excited your puppy is during play, the more likely he is to offer mouth behaviors.
2. Provide appropriate chew outlets, such as rawhide chews , Nyla-bones, frozen food stuffed Kong or Busy Buddy toys, and durable stuffed toys. These toys should be used to redirect your puppy's urge to chew away from your hands or feet. Smearing peanut butter on your pup's toys can also help make them more appealing than your hands. Mouthy puppies should be offered a toy before all interactions with people. This sets them up for success by having an appropriate option to mouth before they even have a chance to chew on hands or feet.
3. Should a puppy mouth your hand, you want to remove any and all attention so that this behavior is not accidentally rewarded. This means taking away eye contact, any touching, and keeping silent. Once the pup has calmed down, you can offer him a toy to start the interaction again, or ask for a "sit" (review Basic Manners training) before giving the toy to encourage a more desirable behavior. In some cases a high pitched "ouch" can be used to interrupt mouthy behaviors. This should be a high-pitched yelp – one that is loud enough to stop the behavior, but calm enough not to scare the puppy. If your puppy looks fearful or cowers you should avoid the "ouch". Also, some dogs perceive the "ouch" as fun and attention and may inadvertently find it rewarding. Avoid the "ouch" if mouthing increases

In some cases excessive mouthing behavior is a sign of fear or stress. Other signs of fear and stress include, but are not limited to body stiffening, cowering, growling, snarling, ducking of the head and showing the whites of the eyes, trembling, excessive fidgeting, and urinating. If the mouthy behavior occurs with these signs or if you sense for any reason that there is an aggressive nature to it, please contact your veterinarian immediately so that you can seek help from an appropriate behavior specialist. Fearful behavior in puppies is not normal and may progress to aggression if not managed appropriately.