Thomas Sutcliffe: Plays aren't films, so say no to slo-mo

I went to see Complicité's new show, A Disappearing Number, this week and – in common with most of the critics – I found it both ingenious and moving, a succession of brilliant theatrical effects that had been sanded flush with the play's purpose, so that they didn't snag at your attention in the wrong way. But it did contain one sequence that made me wince, with the same reflexive jolt you get when silver paper touches a filling. There was a point at which the actors on stage went into slow motion and – as it invariably does when this happens in a theatre – it momentarily made me wish I was somewhere else altogether.

It isn't alone in this, of course. There are quite a lot of directorial tropes that I would happily never see again. Recently, for example, we seem to have gone through a spate of rhythmic percussion on the London stage – a Stomp-influenced fashion that can often be locally diverting (who doesn't enjoy a bit of team drumming?) but which usually strikes you as a distraction from what the play is actually about. But of all these tricks and accessories the slow-motion sequence is the one that grates most painfully. And, coming out of the Barbican the other night, it wasn't immediately obvious to me why that should be.

It can't be anything as straightforward as the disruption of illusion. That, after all, is part and parcel of A Disappearing Number, which actually begins with Paul Bhattacharjee pointing out the unreality of everything the audience is looking at, as compared with the ultimate reality of mathematical truth. So it isn't that at one moment you're thinking of the actors as real people and you're then abruptly reminded that they're just performers, going through the motions (slowly).

Nor is it that actors almost always look stupid when they're obliged to do this, although they almost always do (I say "obliged", incidentally, because I can never see such a sequence without catching a whiff of directorial insistence on the air; can one really imagine any actor saying "I know what might work here... I'll pretend I'm on an action replay"?) But clearly something dislocating is taking place.

My suspicion is that the problem starts with the essentially cinematic nature of the spectacle. There are Oriental theatre traditions that include very slow motion movements – most notably Noh theatre – and it's possible that they are one of the origins of this device. Mimes are quite fond of slow-motion too – its apparent impossibility supplying a useful challenge for their skills – and I suspect they must take their share of the blame, too. But for most audience members and most theatrical practitioners this isn't an allusion to another tradition of theatrical movement, but to another way of seeing, one that is anchored to the moving picture. And since slow motion is almost irresistibly compelling on screen (however overused it has become), it's not hard to imagine a director thinking, "I wouldn't mind having some of that".

The problem is that on-screen slow motion and onstage slow motion travel in diametrically opposed directions. On-screen slow motion, however much it disrupts the naive realism of the scene, is usually an amplification of truth – a device that lets you see things as they are more clearly. Indeed, it may well make things visible that would otherwise be undetectable; the shape of water as it falls, or the precise way in which a flurried action has taken placed. On stage, by contrast, it nearly always involves a departure from actuality – in part because a human body deciding to move very slowly is utterly different from a human body being slowed down by technological means. So, try as they might, most actors' movements become more false and artificial, even as they are employing a rhetoric that we associate with greater clarity. It is, in a straightforwardly literal way, a pretension – one that unhappily reminds you that it's sticking around for twice as long as it should do.

It matters more because slow-motion on screen delivers something both when it turns up and when it disappears, first reining in action and then releasing it again so that we understand its tempo slightly differently. It can be like stepping off an escalator when you're not quite ready and it works because the device is cut from the same cloth as cinema. It reminds us of the clockwork regularity of normal screen time (literally clockwork in the case of the first cine cameras). But on stage the interruption of an idiom from a different art form dilutes the theatrical moment, and when things return to business as usual you simply feel a sense of relief – or I do, anyway. And don't even get me started on theatrical freeze-frame.