Need to know: The mission - Nicholas Barber tries his hardest to fall under the hypnotist's spell, but can he be persuaded to be a Spice Girl?

Here I am in an Edinburgh pub and, by the end of the evening, I intend to be laughing at things which aren't funny, crying at things which aren't sad, seeing things which aren't real and singing along to Bee Gees songs. Nothing out of the ordinary there, you might think, but I am planning to accomplish all this without the aid of alcohol. I will be using only the power of my mind, as directed by the hypnotist Hugh Lennon.

The Physician & Firkin is jammed. Ten other would-be mesmerees and I are sitting in a row of chairs on the section of floor that's marked off as a stage. Lennon asks us to close our eyes. He asks us to let our limbs grow heavier, to visualise ourselves as leaves floating down from a tree. As luck would have it, daydreaming and dozing off are two of my foremost abilities, so this isn't too difficult. "Imagine the person to your right is a soft pillow," he says. "Lean against them, and feel yourself drifting deeper, deeper into sleep ... " I do my best. I don't feel very hypnotised, but on the other hand, I am nuzzling up to a complete stranger in public, and that's not something I normally do, except on the very odd, special occasion.

"When I count to five," says Lennon, "you will be in a desert. You will be baking hot. Your mouth will be dry." And he's right! It's working! "Now," he says a minute later, "you're somewhere freezing cold, and you'll do anything you can to keep warm." Sadly, I'm still hot and dry- mouthed. I have to assume that this has less to do with hypnotic suggestion than the fact that I'm in an over-full pub in August and I've had nothing to drink for an hour.

It's very disappointing. I'm the only volunteer who doesn't go under. Lennon tells the others their chairs are burning, and they spring to their feet. He tells them to forget the number seven, and for the life of them they can't recall what comes between six and eight. Then he tells the girls that they're Madonna, and the boys that they're the Spice Girls, and all of sudden my own inability to join in doesn't seem quite so disappointing.

Afterwards, I speak to one of the volunteers who was luckier/unluckier than I was. He knew that what he was doing was slightly silly, he says. It just seemed like the right thing to do. "When I heard `Jailhouse Rock', I thought, yup, that's my cue to shake my hips. And when the guy asked me which number came after six, I did have seven in my head, but it just didn't make sense to say it."

As for my own failure to go under, I can't understand it. I don't usually require much persuasion to stand up in public and make a fool of myself, and the workmen who flogged me that dodgy carpet a month ago will testify to how suggestible I am. My only theory is that I wasn't relaxed enough to be hypnotised because I was too anxious about whether I was relaxed enough to be hypnotised. What can I say? The next time I'm in a pub and I want to lose my inhibitions and dance like a Spice Girl, I'll have to rely on the traditional method