I have a very good friend, he's 16, he's really nice to me and everyone. I've never seen him say or do anything that was even slightly mean or rude or impolite... he's actually very popular amongst most of my friends... but he's a little childish sometimes, usually only in a specific class we have together when he's with his best friend. In all his other classes, he's very introvert, shy, and just.. seems kind of sad. He doesn't usually stir up conversation with anyone besides me even though everyone likes him and thinks that he's nice and everything... he definitely doesn't appear to have any type of disability when you first meet him. He's even on the football team and is great at basketball! But the thing is, he speaks rather toothily.. and when we have to sit still for a while, watching a documentary or movie or something, I sometimes catch him staring into space. His mouth is usually hung open, and it's like he doesn't notice that it is for a long time. Usually I'll say something to him about the movie or class to get his attention, and that automatically snaps him out of his 'trance'-like state and he closes his mouth... he doesn't have anything wrong with him mentally, that I can see. He acts totally normal, besides the whole "childish" thing... but I'm sure he's aware that his mouth is open sometimes because when he catches himself doing it he looks rather embarrassed. Sometimes he has trouble closing his mouth completely though, but that's only when he closes it without speaking... He's also definitely not dumb. He has at least a 90 in all of our classes, I always go to him for math homework and psychology and stuff... it's kind of hard to explain, and I didn't mean to offend anyone with the title of this question but I was just curious.. I think that it would be very impolite to just ask him "Hey, what's wrong with your mouth?" or "Why do you sit there with your mouth hung wide open all the time?" because he's just very sensitive, believe it or not. I've known him for about 6 months but never was I brave enough to ask about this. It's not an issue, I'm just very curious... so.. my question is,.. what is causing my friend to do this?.. could it be a physical deformity in his mouth? Or something mentally? I know his bottom teeth are somewhat crooked,.. but I don't really know what it could be...