My perfect, darling Al has, on 4-5 occasions with 4 different dogs, suddenly and seemingly capriciously snapped at and pursued another dog. I've had to intervene to break it up. No actual biting as far as I can tell, but it sure looked like he was trying to do actual damage. I have been unable to identify antecedents except in one case where I had him on his back in my lap, checking his paws, and my partner's dog approached (perhaps out of mere curiosity, a very nonaggressive beta dog), and Al may have felt threatened in his vulnerable position. Another time, a much larger dog was sniffing Al (not his butt, I think, more like his penis) and perhaps the other was getting too up-close and personal. In some cases, a lot of things were happening, play and activity, but I did not see the actual start of the incidents. It was very fast.
Can any experts offer advice? What should I look for?
How should I respond? I each case, I've tried to correct him severely, manhandled him a bit, remonstrating loudly and getting right in-his-face, then letting him know we're still buddies maybe 5 min. later.