It is now 50 years since the 1971 publication of William Peter Blatty’s bestselling novel The Exorcist, inspired by a 1949 case of demonic exorcism (it took two priests) that was a news story when Blatty attended Georgetown University in the 1950s. To date there have been two novels, around four films, a television series, a video game and even a 2012 play. There have also been many parodies and imitations, including a cartoon version in 1987 called the Duxorcist in which spirits possess Daffy Duck.