Size Doesn't Matter
This is a fierce dog. I can't tell you his name because I'm trying to be as anonymous as possible here but I will say he is is very fierce. He weighs four pounds, maybe. He is fully grown and a butt. Approach him and he will bite you. I know he's bitten me several hundred times, almost daily or the past year and a half actually but I love him to death.
He's a puppy mill dog. If you ever have any doubts that all the stories about how bad such dogs can be, don't doubt it. They aren't bred for temperament or health only for quantity. Their mothers are started as soon as they go into heat and don't stop until they physically can't give birth any longer. then they are killed, sometimes not so humanely. He is pretty much insane. So reactive that the sight of another dog will send him into a pseudo seizure. His eyes roll back in his head and only the whites show. He foams at the mouth and barks until he becomes hoarse. If he's close enough he will bite, don't doubt that for a second. If he can't bite the dog and you are close enough he will bite you, repeatedly.
Fortunately for all involved he really doesn't have the jaw strength to do any harm. It's like getting a big blood blister. Unfortunately for other such dogs they can cause harm...big time harm. It isn't their fault it's the fault of those who bred them but unlike others who say there aren't any bad dogs only bad owners...I disagree, there are bad dogs. Like this one. He has hips that are like swiss cheese, one has been replaced already. His teeth will all fall out eventually. His trachea collaspes and he chokes to right it. He's a mess and there is nothing I can do. Fortunately he landed in a home that can afford to help with his physical problems and has the sense to shield him from emotional ones.
So when you see that adorable puppy in a pet store don't buy it. It isn't worth the cost to you or the dog.