So, most people know The Exorcist was based on a novel. What most people don't know is that that novel is actually based on an actual exorcism that occured in 1949. I found this article on the fact and fiction regarding this right here: The Haunted Boy It is admittedly a huge article, but it is very interesting and creepy. Particularly haunting for me was the priests' recounting of images of Satan burning into the boy's skin. Whether it was a real possession or not, this article doesn't say, but there was certainly something very wrong with this boy. By the way, I've never seen The Exorcist in its entirety, I really want to now, though.