The new film "The Rite" (opening Jan. 28) follows a skeptical seminary student who is sent to study exorcism at the Vatican. An Italian priest and veteran exorcist (played by Anthony Hopkins) befriends the student and teaches him the craft of demon displacement.

The film's poster art takes pains to assure audiences that the film is "inspired by true events," presumably because audiences would be less interested in a wholly fictional story about exorcisms .

The "based on true events" tagline has been a staple of countless horror films, including "The Texas Chainsaw Massacre" (1974), "The Exorcist" (1973), "The Amityville Horror" (1979), and "The Haunting in Connecticut" (2009). It seems that anything about evil tagged with "true story" is guaranteed to double box office sales. [Monsters, Ghosts and Gods: Why We Believe]

More often than not, the "true story" bears little or no resemblance to anything in the film. For example William Peter Blatty's novel "The Exorcist" was based very loosely on the story of a 14-year-old Maryland boy who underwent an exorcism in 1949. That much of the story is true; virtually all of the gory and sensational details, however, were wildly exaggerated or completely made up.

Along with a handful of Vatican-sanctioned exorcists, hundreds of self-styled exorcists supposedly help people cleanse themselves. Michael Cuneo (author of "American Exorcism: Expelling Demons in the Land of Plenty," Doubleday, 2001) found no reason to think that anything supernatural occurs during exorcisms. After attending 50 exorcisms, Cuneo is unequivocal about the fact that he saw nothing supernatural. No spinning heads, levitation, or poltergeists were on display, though many involved some cursing, spitting, and vomiting for good measure. [Related: Ghost Stories Haunt American Culture]

So what are the "true events" that "The Rite" is based on? It's not at all clear; on the film's official website under "True Events" it simply features links to a dozen or so generic news stories about exorcisms, not to any specific, spectacular cases demonstrating demonic possession.

"The Rite" is based on a nonfiction book by writer Matt Baglio, who attended a Vatican-sponsored seminar on exorcisms and shadowed a California priest who became an exorcist. It seems likely that the "true events" in the film are limited to the fact that priests are taught to perform exorcisms, and occasionally do them. Anything involving levitation, supernatural strength, or spinning heads should be taken with a grain of salt, which you'll probably want on your popcorn.

Benjamin Radford is managing editor of Skeptical Inquirer science magazine and author of Scientific Paranormal Investigation: How to Solve Unexplained Mysteries. His Web site is www.RadfordBooks.com.