We recommend the whole article,"The Exorcist': 10 Creepy Details From the Scariest Movie Ever Made" as an entertaining read, but thought that one of the "creepy details"---how Academy-Award winning actor, Mercedes McCambridge, created the demon's unforgettable voice---would be of particular interest to our followers.
(Hint: It wasn't all technique; there were also raw eggs, cigarettes and Jack Daniels involved.)
Thankfully most voice actors we know don't require priests on set, but you have to admit that this is some serious commitment to character!
Inside Movies: “I tied her hands behind her back. And she would do the dubbing a line at a time, and often she would ask for more booze and more cigarettes,’” the director said. “What would happen to her voice is you sometimes hear a wheezing sound in addition to the words. That came out of her throat."