I had an idea that a game based on this movie would work well for PBP, but not in person. In person, other players could see if something is up. (notes being passed, failed dice roll, etc). In PBP, a private message is passed and no one is the wiser.
Hmmmm....I'll have to think about this a bit.
If you don't know which movie Ive referred to, John Carpenter's The Thing (and prequel).