Hey, just a few interesting thoughts.
First, if you have not seen the movie the Exorcism of Emily Rose, I highly recommend it. It is loosely based on a true story, and I found the enactments of possession to be very believable, not gratuitously gory or physically impossible. If you get freaked out by the subject matter, then don't see it, or see it with a good friend.
And, secondly, last night I attended a Catholic social event involving a bonfire, smores (*drooling*) and a talk by an exorcist. The priest made an interesting observation starting off the night. He said that demons hate the fact that human beings can reproduce. Angels and demons are not sexual beings and cannot reproduce their own kind. Therefore, they seek with especial vehemence to pervert human sexuality and reproduction. Wow. That makes sense.