Yes, I have had dogs all of my life. Was your son bugging him (like with a toy, while the pup was sleeping or eating?) Because it didnt break the skin and was more of a warning, it sounds like the pup was agitated. Maybe have a chat with both (not trying to be funny) asking your son what he was doing before hand to the pup (if anything). Sometimes, younger children like to pull ears, tails, lift jowls etc. The reason I ask is it sounds like the pup was just tryong to say “enough, I dont want to hurt you, please leave me be. Hope this helps. Hugs.