On the underside of my tongue, there are two very small 1/4" flaps of skin about halfway back that sort of hang down. I saw someone mention below that he had those, and he wondered if they were abnormal, so I guess not everyone has them, but... one of mine seems to be infected somehow. I don't even know how to describe what it is if you don't know what I mean, but it hurts like a canker sore, and it's red, and for as small as it is, it's packing a punch.