I think you're onto something there, MOFF. It sounds like something regarding the vets', the smells, noises, flashbacks to unpleasant memories of painful experiences, harsh discipline etc., is triggering this response. Did they do any temperament testing at the shelter? Usually it is required. I would be a bit on guard when introducing him to new people and places until you can narrow down the situations that bring about this reaction. I'm sure he's having a huge adjustment right now. I'd make sure he's smothered with tons of positive re-enforcement, praise and rewards for positive responses and behaviors. He sure is a beauty!! I wish you the best of luck with your new addition!! Hang in there!