Mouthing: Do you have a puppy that would rather use your arm than a bone as a chew toy? While it is normal for puppies to use their mouths when playing with each other, this behavior becomes a problem when it carries over into their interactions with us.Many breeds are genetically inclined to use their mouths to do a job. Sporting breeds are the retrievers and the carriers of items. Working and the Herding breeds use their mouths to control the movements of humans or other animals. Terrier breeds are motion-activated and will chase anything they perceive as small rodents, including your feet. Understanding these tendencies in your own puppy, whether a mixed breed or purebred, can help in dealing with the problem of mouthing.