Probably from the blood. I would also wonder if maybe he doesn't have an infection? Plus he may be keeping leftovers in there - if your in pain cleaning is not easy and just makes things hurt more so he's probably not doing a great job. I can't stress this enough protein is important to healing. If your making soup buy some unflavored protein powder and put a scoop in his bowl. It will add calories and vitamins and as I said promote healing. Hugs.

Oh btw salt probably stings (my tongue was really sore too) if you are cooking for him go lightly on the salt and just add it to your food.