We have a puppy thats approximately 6 months old give or take some. Showed NO signs of aggression, hes pretty much scared of us as if we want to beat him, he lays down. He's not small, like our other small dog, a little bigger than a chihuaha (mut). They play together, she growls at him when he messes with her even though she he is twice her size easily. Today we were picking them up from the in laws, and they have a male rat terrier, that doesn't get along with other dogs. Our puppy, which is bigger than him, kept trying to play with him and "smell" him as all dogs do. At least 5 times the rat terrier would snap at him and chase him a few feet. Our older femal dog went by him and the rat terrier snapped at her, well our puppy went and attacked him and had him pinned down, it took me and my girlfriend to pull him off before he would stop and the rat terrier limped away crying. He wasn't bleeding or anything, just limped for about 3 minutes before walking normally again. The fiance is scared he will do this to our female, but I am trying to tell her he sees her as a mother I feel since hes been with her since he was 6 weeks old and small. (even though her little head sits in his mouth as he plays with her while). What would you say? something to be worried about?