We’ve got a miniature breed puppy, aged 4 months. She’s very bitey. I can’t tell if it’s teething or is starting to become aggression. She can really hurt. She growls sometimes when she’s nipping our hands. We have tried yelping when she does it, but that makes no difference. We walk away and that makes no difference. Is this normal puppy behaviour? We’ve had puppies before and they haven’t been as bitey as this