You know, I do kind of wonder if she is more tolerant than some other dogs might be in this regard - she (Li'l Girl) doesn't snap at him (Hairry) or otherwise react negatively when he starts to bite; she just kinds of holds still and stops playing. I guess that would be a form of the "withdrawal" you were talking about. The "vibe" my husband gets is that she is not comfortable with it. He stops, and they go back to playing. We've also talked about aggression and neither of us thinks that's what's going on. (In fact, in all my years of having/working with dogs, I can't remember when I had/dealt with one who was so affection-loving! I think "love sponge" is the term!) Also, the people at the shelter told us that the person who surrendered him said he was "crate-trained", which I think can mean different things to different people - we don't know how much time he may have spent in a crate (all day while his people were at work??) and how it may affect the way he interacts with other dogs. (They said he was a victim of a divorce, and the spouse who had him did not have a place to go where s/he could have a dog). So anyway, we will contniue to monitor these two! Thanks again for your comments and advice!!