Janet Leigh as Psycho victim

If you've never seen Psycho, don't let the first half hour disappoint you.

You need the patience of a Sixties audience to sit through what is a slow meandering start focussing on a story of stolen money that never gets anywhere.

Hear the blood-curdling scream from the famous shower scene

Even when the fabled Norman Bates finally appears, his scenes with Marion Crane, played by Janet Leigh, are much too wordy. The innuendoes come so thick and fast, we seem to be watching Carry On Schizophrenia rather than a cult movie classic.

Yet it's precisely because of this playfulness that I love the film. Of course, we can gasp at the hideousness of the shower scene until we're as blue in the face as Janet Leigh becomes.

But without this extra layer of cinematic mastery, without Hitchcock playing puppet-master manoeuvring his audience's reactions, Psycho would be nearly as banal as the many slasher flicks it spawned.

In other words, without that lengthy, taut build-up to poor Marion's demise wouldn't be half so memorable. So if you tire of the stolen loot sub-plot then that's probably the point.

Stashing stolen loot: a Hitchcock red herring

It's the work of a director manipulating our emotions in one of his most black-humoured "McGuffins" (his famed red-herring plot device). And if Norman Bates seems an overwrought bundle of sexual repression, then that's because Hitchcock could think of no better kind of cinematic toy to have fun with.

In Norman he created the ultimate talking point - an anti-hero despicable in his melodramatic actions, but a lot more real than society would care to admit. It's that kind of taboo that made Hitchcock laugh.

Visual adventure

What complements this narrative black humour is the visual style of the film. One only has to compare it with other Hitchcock thrillers to see that this was more of a technical adventure than previous projects.

Initially intended as an episode of the TV series Alfred Hitchcock Presents, Psycho was lengthened into a feature film but still used the TV crew and materials. That's why it looks so sleazy.

Hitchcock: manipulated audience's emotion

There's no colourful canvas of glamour as in To Catch A Thief or North By Northwest - this is claustrophobic and black and white. There's not a handsome leading man in the vein of Cary Grant or James Stewart - just a previously unknown, fragile looking actor called Anthony Perkins.

Committing Hollywood hara-kiri

Even in its structure it commits Hollywood suicide by having its leading lady killed off in the first reel. But what on paper sounds like arthouse fodder is actually what makes Psycho so arresting on the big screen.

It may be as manufactured as any other movie, but what your parents may have first witnessed in darkened cinemas was something more hysterically warped than had ever been seen before - and, nearly 40 years on, has rarely been seen since.

Movie folklore may well have superseded the intellectual substance of the picture.

It's a common film buff anecdote these days that Hitchcock may not have directed the shower scene (some say it was titles director Saul Bass) and that audiences weren't allowed into the cinema once the film had started.

But to experience the undeniable challenge of actually watching the film is to discover the founding reason why Psycho is still the most clever horror film ever made and why the phrase "A boy's best friend is his mother" has never been the same since.