Just noticed a crusty area just under my cat's chin. It was stinky as well. He let me clean it and there's a little hole. Doesn't look like a bite mark. I think maybe a burst abscess and the crusty stuff was dried pus. He's perfectly fine eating and happy. He was fine while I cleaned it. No crying or distress. He's currently sleeping contentedly on his bean bag. I've never had this before.. does he need a vet trip?