How was it for you?

The audience was stirring uncomfortably. The opening titles had played out over a series of shadowy shapes writhing behind semi-opaque screens. Now we were in the movie proper, entering the first scene. The tone was being set; we were looking for clues as to what kind of a movie this was to be. And we were watching... oh good God... full-on shagging.

The cinematography was soft-focus, the score was all sultry strings, and the woman was astride the man. Nervous titters started breaking out in the cinema. Even in the dark, one could sense a collective blush. This was the Norwich Odeon after all, not some tacky dive in Soho. Something was wrong.

Then the woman reached for a scarf. The strings darkened. We hesitated, still squirming. The woman tied the man's hands to the bed. As they were reaching climax, out of nowhere she produced an icepick. We watched her stab the man again and again in a horrific, bloody frenzy. We all breathed a sigh of relief. This wasn't porn after all, it was a violent thriller. We could live with that. We settled down to enjoy the rest of Basic Instinct, now that order was restored.

Moviegoers can, with varying degrees of comfort, sit through explicit depictions of mutilation, dismemberment, decapitation, disembowelling, and take it in their stride. But show them a graphic sex scene and a whole different kind of queasiness can set in.

And it's not hard to figure out some of the reasons why. In mainstream movies, violence advances the plot; sex generally brings it shuddering to a standstill. Film has always had to strike a balance between narrative and spectacle - take the Alps at the beginning of The Sound of Music. The camera swoops and dives through gorgeous scenery, we drink it all in, then just at the right moment, the music swells and up pops Julie Andrews to kickstart the narrative. The sex at the beginning of Basic Instinct is like the Alps: it's an establishing shot, after which the music swells and up pops Sharon Stone. But ladle on the scenery too thick, and impatience sets in.

Then there's the voyeuristic nature of cinema itself. During the ascent of film studies to the status of academic subject, some joker hit on the idea of applying the theories of Sigmund Freud to the act of watching movies. And here's one of the ironies of 'adult' cinema: Freudian film theory argues that the pleasure of watching movies has a lot to do with our re-experiencing infantile urges while sitting in a dark auditorium. Essays have been written on how we as viewers re-enact 'the primal scene' - Freud's phrase for that symbolic moment when the child stumbles upon his/her parents having intercourse - and how all physical action in cinema is a metaphor for the sexual act (I'm condensing outrageously here). If this is true, and we experience all action scenes as sexual on some level, no wonder watching a literal depiction of the sexual act can make us uneasy. It's too much, too direct, especially in a social setting. It raises the spectre of a taboo. Maybe that's why sex and violence seem so inseparable; that troubling act of voyeurism must be cancelled out with violence. And ice-picks.

Arthouse movies have more licence to confront these things head-on; often they thrive on creating discomfort. And with the added bonus of a looser approach to plot, the arthouse gives sex more room for manoeuvre. Last Tango in Paris and In The Realm of the Senses achieved notoriety in the 1970s for their forthright approach to sex, but both plots ended in a murder; more recent films, like 9 Songs and Shortbus, try to move things on by doing away with the violent ending. Which is interesting. Except that it isn't. It's dull.

It's no coincidence that Hollywood slackened its plotlines around the same time that film censorship became more liberal, in the early 1960s. There were major pluses - more focus on character, less predictability - but it could be argued that thrillers, and especially film noir, of which Basic Instinct aspires to be a modern example, never quite recovered. Those plots will keep powering down while the protagonists indulge in a bit of athletic trysting.

Not that sex doesn't belong in movies - of course it does, and it can be entertaining and titillating. Hell, it can even advance the plot. But sometimes it's worth trying it with the lights off.

Nick Riddle