After I taught Sharav as a puppy that biting was unacceptable, he came to find it so objectionable that he would literally pull his mouth away if a person’s hand was inside it.
I sometimes demonstrated this to curious onlookers on our walks by holding his mouth open and putting my hand inside it, then letting go and showing that he would pull away, but I don’t recall a time when anyone else volunteered to try it.
Showing off his teeth. New York, August 2018. Click any photo to see more.