I am not a behaviorist by any stretch of the imagination, but I am sure this sort of thing is completely normal and probably happens a lot. Knowing how the play growl upsets Tasha, I guess it will put a little bit of a damper on your play sessions with Tommy and you will need to be careful from now on. I really wouldn't worry too much about it at this point. My Ripley feels very protective of me when he is on my lap and his Big Cousin Dale comes over to see me. He will show Dale his entire set of upper teeth although that's about as far as it goes and Dale backs up. Actually it is quite funny when it happens, since Dale is about 75 lbs. now and Ripley is 15 lbs. and Dale really respects the little guy. When they are both down on the floor together they are fine - it's just when Ripley is on my lap and he feels the need to *protect* me.