Bitsy has never growled at anything. Buster shows his teeth to the cats if he's having mommy time and one of the cats try to hoard in, but he gets scolded. We laugh more then anything because he is missing some teeth (including both k9's), and he looks so funny. Charlie on the other hand hates his nails clipped and will growl when we are clipping them. If he's being bad we use a muzzle. If he's good while we're clipping them then he gets a biscuit, if he's bad he gets the muzzle on (which he hates) and no biscuit. He knows now and usually behaves well.