The greatest thing to come out of Catholicism since Pancake Day, The Exorcist is re-released for its 50th anniversary. It follows a famous actor (Ellen Burstyn) who moves to Washington DC, where her 12-year-old daughter’s (Linda Blair) telekinetic temper starts turning heads among the local intelligentsia.

Mere months after William Friedkin’s Death, the director’s masterpiece remains embedded in the public consciousness like pea-soup vomit on fresh linen sheets. The possession movie to end all possession movies, its body-contorting special effects have been done to death since their first display in 1973. And while Friedkin literally throws everything at the bedroom wall, it is the detail, characters and economy that make The Exorcist work where so many imitators flounder.

For starters (and I’m not talking about soup this time), the film breezes past how Regan came to be possessed in the first place. As in William Peter Blatty’s novel, we are spared her Ouija board-playing antics and therefore the most mechanical and ultimately irrelevant part of the story. Burke Dennings’ (Jack MacGowran) death is also kept off screen, and made all the more horrible in our imagination.

MacGowran is hilarious as the drunken Dennings, with human performances from Jason Miller as Father Karas and Linda Blair evoking a desecrated Shirley Temple. These colourful characters help ground the film in reality, making the supernatural horror show completely believable. A devil for detail, Friedkin’s techniques ranged from eccentric (making the set freezing in order to see the actors’ breath, firing guns to scare them) to downright psychotic (tying Mercedes McCambridge to a chair and having her swallow raw eggs to produce Regan’s demonic voice).

The exorcism itself is probably the least interesting part of the film, which turns out to be named after its most minor character (see also The Wizard of Oz and JFK). The terror is in the buildup, Hitchcock style. When Regan first tells her mum the bed is shaking it gets a cute laugh. By the time she starts masturbating with a crucifix, you wonder how Warner Bros. let them get away with it.

We’ve all heard the stories of scandalised 1970s audiences running straight from the cinema and into the nearest church. And of course the movie’s immediate impact is diminished a half-century later, thanks largely to cultural freedom from the stranglehold of Christianity (few people today are scared of Satan). But The Exorcist is still shocking in its brutality and haunting in its imagery, whether taken as a literal struggle between good and evil, or an exorcism of parental paranoia.

This is another horror film about inter-generational struggle, a society afraid of its own youth. It is a meditation on guilt, reflected in Regan’s mum for her divorce and Father Karas over his own mother’s death. Or it is simply a coming-of-age story, a girl gaining independence from her mother and becoming her own person/demon. And given its theme of innocence corrupted, the Washington DC setting is no coincidence. Blatty moves medieval superstition to middle-class, modern-day America, specifically to the seat of government (as copied by The Omen).

From its revolutionary use of Tubular Bells (the basis for John Carpenter’s Halloween theme) to visual effects that put the bed in bedlam, The Exorcist invented and transcended a genre. 50 years later, it still has the power to make your head spin.