Ever wonder why...

Why is it that when you have a sore in your mouth, you just can't leave it alone? For example, I accidently bit my lip last night, so there's a sore spot just inside my mouth. I've been continually running my tongue over it, and feeling it. And it hurts! When I have a bruise somewhere I don't keep pressing it to see if it hurts, so what's different about my mouth?

It's like going to the dentist, and they put that suction thingy in your mouth, what's the first thing you do? Feel it with your tongue and ZHOOP it sticks to the suction tube. I think tongues simply have a mind of their own. And they aren't very bright.