Why Sans' Room is ALWAYS Locked

So speaking of fricken' UNDERTALE, I heard of the Sans' being a human theory. It's not really all that to me anymore because Im already used to him being all bones. Just a being of sexy bones. But that's not the point. The point is, that there are little hints and coincidences that say Sans is still a human being and that he only dressed up like that so that his brother, Papyrus, who's a real skeleton, wouldn't be lonely. Seeing as he loves his brother very much, this isn't very surprising to me and the theory is sweet in a way. 

Theory hints:
Sans bleeds, Papyrus does not. 
Sans is bigger (not cuz he's big boned )
Sans has very little bone to show other than his face and hands. The rest is covered, wearing a rib-cage shirt? and some socks...
Sans has pupils and his brother does not. 
Also Sans' mouth doesn't move when he talks (or his mouth doesn't open...). It's like he's wearing a mask.

i think that's it....

Anyway, I'm sure that's not even enough evidence, but I just think it's fairly interesting...so I just like it and decided to draw this. 
enjoy-

copyright to toby fox

thanks for the game bro omg