Hm
I just tested this with two different dogs in my vet clinic and see no distortion. It also wasn't reported by anyone else.
Could you try repairing your game by right clicking on the game in Origin and hit repair game and also delete the localthumbcache file in your doc folder.
I think this distorted petting and hugging (also with other sims/toddlers) happens occasionally if the game has routing problems with the two sims involved. In my game it happens frequently when parents and toddlers start the long "play" animation.
