Remy's Bump

When I got home from work yesterday I noticed Remy has a bump on the side of his head, you can see it between his eye and his ear . He acts like he feels fine and isn't showing any symptoms otherwise. I'm not sure if he hit it on the cabinets when they were playing inside or if he got hit by a stick they play with outside. Poor Rem. Abby's always beating up on him.