It’s that old Penn and Teller sketch. First you show them how it’s done - how it’s usually done, how those other schmucks would do the trick - then you do the trick again, only this time you do it differently, better, and with such élan, such verve, that no one’s going to work out how you did it, even though you just told them how. Oh, and just like Penn and Teller, make sure you add a bucket-load of fake blood into the bargain, just to seal the deal.

The Last Exorcism tells the story of Reverend Cotton Marcus, a man from Baton Rouge, practically born into preacherdom, whose faith was shaken by the near-death of his only son (‘The first thing I thought of to say was, “Thank you Doctor” not “Thank you Lord”’). As we meet him, he’s been reluctantly carrying on the family business of spreading the Good News and exorcising evil spirits, all the while telling himself that he was at least performing some psychological good, even if he no longer believed in the letter of the ancient screeds he spouted.

Having resolved to quit, he accepts the call for one last exorcism, this time taking a documentary film crew along with him in order to expose all the little tricks of his trade to the world. So we see him setting up wires in the bedroom of the girl to be exorcised, little hidden loudspeakers to emit demonic wails and moans at just the right moment, even showing off the smoke-emitting ducts on his crucifix. But when Cotton Marcus gets to the Sweetzer farm in rural Louisiana, he finds himself face to face with a little more than he bargained for.

Coming from the production stable of Hostel director Eli Roth, The Last Exorcism, predictably, has its fair share of moments to be labelled ‘not for the squeamish’. Director Daniel Stamm similarly took the mockumentary format into macabre territory with his 2008 feature debut, A Necessary Death, which claimed to follow the final preparations of a suicidal volunteer. Under his hand, The Last Exorcism is clearly as comfortable manipulating its audience’s emotions as it is manipulating its own generic format. As with The Blair Witch Project, however, one can’t help but feel that, were you to strip away the shaky cam conceit of the frame, you’d be left with a remarkably formulaic script. That is not to say it is not grimly effective.

In the end, perhaps the most consistently disturbing feature of this film is not the apparently psychotic teenage girl, or the demon that is supposed to be possessing her, but her control freak fundamentalist father. And it is in the light of this that The Last Exorcism is very much an Exorcist for our times. For the Reverend Marcus’s attitude towards his profession is, to a large extent, that of every one of us, in these decaffeinated, supposedly post-modern times. We all know very well that the big Other does not exist, that democracy is a sham, that our actions at work and in the supermarket are contributing to the wholesale destruction of the planet; and yet we carry on, operating under the flimsy protective gauze of a layer of reflexive cynicism. It is not the gods that we ourselves believe in that we fear, but the - always more fanatical, always more fundamentalist - belief of the other that threatens us. And so we cross ourselves and vote for measures that curb our own freedoms and perform our little absurd rituals in order to protect ourselves from the other’s belief, fully aware that it is only these futile litanies that keep the threat alive in the first place.

Robert Barry