In many cases your imagination is much more effective than what can be shown. It primes you to know something is about to happen - the anticipation and anxiety is worse than what ends up happening.
Oren PeliAfter I watched 'The Exorcist' I refused to watch any other movie that had anything to do with ghosts or demons. I didn't even watch 'Ghostbusters' until I was much older.
Oren PeliFor a found-footage-style movie, there's a definite advantage in using unknowns, because it helps sell the illusion that it's real. A known actor would get in the way of the suspension of disbelief.
Oren PeliI think the traditional explanation is that demons just find someone, they pick on them and try to break down their spirit so they can... take control of their bodies. Why exactly? I don't know.
Oren Peli