INSIDIOUS: MORE THOUGHTS

CONTAINS SPOILERS

In the way that a meal shouldn't, Insidious has stayed with me for a whole week. The effects of most movies, except the very, very best ones, tend to fade: obviously you still remember them, but the immediate feelings dissipate as life continues and other things demand your attention. You might see a terrific hour of standup comedy but you won't still be laughing a week later at the gags.

But it's been a week and Insidious won't go away. More impressively, it's actually gained in power, the power to unsettle not just while it's running through the projector at Cineworld, but late at night when you're alone in the flat and you've got to walk through to the bathroom then to the bedroom. You can't even put Classic FM on as an aural distraction because suddenly there's that nagging fear that halfway through brushing your teeth the radio will start playing Tiptoe Through The Tulips instead of that nice calming bit of Grieg. Of course it's ridiculous: in broad daylight the idea that a clawed red-skinned demon or a spectral hag is lurking just beyond my peripheral vision. But daylight shows everything that's there; darkness hides everything that could be there. And when the lights go out, anything could be there.

So why does the movie work so well? Well, it's working on our most primal fears: you're not alone in your house, there's something wrong with your child, the world is not as you thought it was. The idea that there's "someone" invading your home who means you unspeakable harm, and it doesn't matter how many locks, bolts and alarms you put on the front door. The idea that a loved one is suffering and there's nothing either you or the doctors (or priests) can do to help them and you have to trust the word of people who could at best be described as eccentric. And the idea that your nice, safe preconceptions of the universe, a universe that doesn't include demons, spirits and monsters, are wrong: the idea that there might be things out there we can't see or comprehend. What's surprising is how many horror movies fail at these relatively simple and well-known ideas.

And it's working on common fears. None of us have experienced vampires or zombies, none but a very, very few have encountered an axe murderer on the rampage, or have been chained by the ankle to a U-Bend and given a hacksaw. But we've all jumped in shock as someone or something has made us jump. We have all heard an odd noise late at night and it's never turned out to be anything but harmless. For all the fascinating and repulsive imagery in Clive Barker's Hellraiser, for all the hammer murders and corpses under the floorboards and weirdly beautiful demons, the most painful moment is when Andy Robinson gashes his hand on a nail, because we've all done that or something like it.

The other big surprise about Insidious is that it comes from the makers of Saw and Paranormal Activity. But it's as if they've taken the found footage of the PA movies and then made a horror film in the same vein. The PAs were generally pretty dull: long build ups, brief jumps, long build-ups, brief jumps. But while you were constantly scanning the blurry video images looking for the slight movement and being rewarded with the tiniest frisson as the door might have opened a fraction of an inch or the saucepans might have gently knocked against each other, Insidious has its demons up front and centre from the start, and they're not coming all the way back from beyond the grave just to switch your lights on and knock things over, they've far more malevolent intentions on their minds.

The result is that you're trapped in that delicious and all too rarely explored no-man's-land of horror: caught between Must Look and Can't Look. You have to look all round the screen at the same time as trying to look away from the next scary thing. When Tucker starts looking through his coloured filters, we know that the next one is going to show something the previous one didn't - we want to tear our eyes away but we can't: we're peeking through our fingers, looking while not looking.

I've had no such trouble with other horror movies. Unless it's spiders or sexual violence I'm always okay with whatever they put on screen. No matter how sadistic the Saw movies got, or the Hostels, or the Friday The Thirteenths, they never unsettled me for a second: I enjoyed them (or not, in the case of some of the later Fridays) but I never looked away and I never felt that special chill once I turned the lights out a week later. I'm feeling that chill a week after Insidious: the darkness is hiding more than it did before I saw the film. That's its triumph. So I'm not that bothered when it drops the ball in the third act: when the demonic forces are invading our world it's far more powerful than when we invade theirs. Frankly I can live with the slackening grip and forgive the slight anticlimactic feeling in the final stretch. When I'm still wary to turn the lights out a whole week later, it's done something right.

Or maybe I'm just a wuss.