I'd also think he ate something and it got stuck in his teeth, got stung/bitten by a bug, or got into a plant in the house or yard.
Open his mouth and check his teeth thoroughly paying special attention to between them. If there's nothing like that then go around the mouth and look for any signs of stinger or bite. Then take a walk around the house and yard to see if any plants have been nibbled on.
Good luck and keep us posted.
Open his mouth and check his teeth thoroughly paying special attention to between them. If there's nothing like that then go around the mouth and look for any signs of stinger or bite. Then take a walk around the house and yard to see if any plants have been nibbled on.
Good luck and keep us posted.