[HELP] Can anyone tell me what might be going on with my dogs lip? Picture inside.

http://ift.tt/2qUSOr5 noticed this last night and cleaned it up with some warm water. Today seemed to be more dried pus in the area. He's not showing any symptoms of discomfort, fever, loss of appetite, etc. No weird smell coming from the area and he doesn't mind if I take a damp washcloth to it. via /r/dogs http://ift.tt/2seLI4D