Reminds me of a story my Dad used to tell.  This is long enough ago the hired hand actually lived with us.  They were going someplace in the car, Dad and hired guy in the front seat, with my little brother sitting on his lap.  Brother started to fuss.  The big old collie, standing flat footed on the ground, reached in through the window and put it's mouth around the hired guy's arm as if to say "You hurt him, I hurt you."  Didn't bite or break the skin, just a threat.