I'm thinking that demons have sort of been explained as souls tormented to that point and are represented by black smoke. In order to be walking around they seem to have to possess somebody. Even Lilith had to possess a body and she was top ranking for a while there. I'm wondering about Sam. Back when he killed Lilith, he ended up with black demon eyes in his own body. If his soul has been as badly mangled as Death confirmed, I can picture his soul tormented enough to be a demon. Maybe a tormented soul has to participate in ongoing evil even in hell to become a demon. With Michael and Lucifer beating on him, he probably didn't get a chance to do much participating in anything except his own torment. His soul was still white light when Death brought it back not black smoke.
What if Sam's soul all in one piece would be a demon? He'd be the only demon that I can think of in possession of his own body. He'd be sort of an uber demon if that's possible. How would you get rid of him short of killing him with the Colt, Ruby's knife or being fried by an angel? Could a demon be exorcised from it's own original body? Sam would be walking around in his own bones making it difficult to burn them short of setting Sam on fire. I guess I'm wondering because if this happens, Dean will feel like he's responsible to deal with it and there isn't one of these options that's even remotely acceptable. It's all pretty horrible. Could Dean even get close enough to do anything about it?
Probably not something to worry about but with all the season promo stuff with Dean with a halo and Sam with a snake I do anyhow. Maybe the snake is the temptation to scratch at the wall. Maybe Sam's already been as evil as he'll get. I guess we'll find out.
For me, speculation is part of the fun with this show.
Can I also say that Death and Tessa are some of my favorite characters from previous episodes? I miss Crowley though.
OK, I'm gonna be quiet now....