The ins and outs of sex at the cinema (on screen, that is)

The really wild shows: Shia LaBeouf (left) and ‘9 Songs’ (right) (Getty Images)

The actor Shia LaBeouf, a man whose name is wrong in so many ways, takes what used to be called method acting seriously.

To play a moonshine peddler during the Prohibition years while filming Lawless, for instance, he ladled rotgut whisky down his throat. Now, he's approached Lars Von Trier to asked if he could have a big part in Nymphomaniac, the unsavoury Danish director's new movie starring Charlotte Gainsbourg.

He sent Larzh a sex tape of himself pleasuring his girlfriend. And, he told the talkshow host Chelsea Handler, it got him the job. Anyone who's seen footage of the talk show can tell he was just kidding – but who knows what's true anymore?

Von Trier is keen to suggest that the sex scenes in Nymphomaniac will be real and authentic. Last time we heard from the effortfully controversial Lars, he was telling the press, "I understand Hitler… OK, I'm a Nazi", and later claiming he was joking. And now he's being terribly wicked again, promising that he's using real sex.

But isn't that terribly old hat? Connoisseurs of non-porn mainstream cinema may have seen Keiron O'Brien and Margo Stilley going all the way in 9 Songs, the two homicidal Parisiennes enjoying grim but verité penetration in Baise-Moi, the auto-erotic calisthenics of Shortbus, the hard-to-fake-it blowjob in Brown Bunny.

They will also know, Lars, that the best sex scenes (between Donald Sutherland and Julie Christie in Don't Look Now, for instance) might leave you wondering how much acting was going on – but they could never be improved on by mendacious assurances of realism from a director or his incorrigible scallywag of a star.