Last week I was in PetSmart and there was some dog there, 10 mos. or so, and I asked the owners if he was socialized and friendly with other dogs. They said, absolutely! Champ barely approached him and the other dogs started growling and bearing his teeth. Plus, there's a rottie in our training class and for no apparent particular reason, he always barks at Champ. I was thinking he was being playful, but his tail isn't wagging or anything (Champ's tail is, of course)...he just looks downright angry. At the dog park, there are dogs that just know right off the bat, that they don't want to play with Champ, and if Champ tries, they get pissed. What do they sense when they get so agitated?