ILLUSION / Right before your very eyes: Penn and Teller do magic, but the real trick is that they like to give the game away. Kevin Jackson met them

NEXT time you find yourself nibbling anchovy paste dainties at a Women's Institute high tea and the conversation is becoming a trifle dull, here's an amusing gimmick you might care to try. Hide one of those small plastic containers of UHT milk in your left hand, and with your right hand raise a fork towards your eye and start playing with the lower lid. When you're quite sure you have everyone's attention, jerk forward, bring your left hand sharply up to your eye, pierce the foil seal, squeeze and emit a blood-curdling shriek. White gunk will squirt everywhere, and your table companions will faint, retch and, if you're very lucky, suffer cardiac failure.

'It's sensationally effective]' beams the co-inventor of this emetic little stunt as he demonstrates the finer points of eye / fork co-ordination. He is called Teller - 'My driving license says NFN Teller; the letters stand for No First Name' - and he is the slighter and more reserved half of the American comic duo Penn and Teller. They might reasonably be described as magicians, were it not that they respond derisively to the slightest mention of the word, and hold the Magic Circle (and its transatlantic counterpart, the Magic Castle) in profound contempt.

'Magicians have this really condescending attitude towards people,' sneers Penn, the large, garrulous, extraverted one. 'They're the only entertainers who draw an 'us and them' line. Magicians are like this: 'Here's a quarter, now it's gone, you're a jerk, now it's back, you're an idiot, show's over'. We thought that if we wanted to do tricks at all, we had to make up for all the silliness that had gone before us, because the second that you start to do magic people think you're a condescending, talentless asshole.'

So Penn and Teller have tried to short-circuit such irritation with a barrage of bloody shock effects and mordant parodies of the hackneyed routines: when they do the old 'pick a card' routine, it ends with both the card and Penn's hand impaled on a knife. When last on British television, they appeared to hack up a live snake into gory chunks and made haricot beans plop out from behind their eyeballs. But all this is timid stuff compared to some of their other tricks, which have included Penn playing around with a bear trap and Teller being run over by a ten-ton truck. They took the deceptively bland title of their 'Refrigerator Show' tour from its opening scene, in which a giant freezer fell down and crushed them.

More shocking to the old guard of stage magic than any of this savage clowning, however, has been Penn and Teller's gleeful way of giving away their secrets - not just to minor pranks like the eyeball-popping routine, but to the staples of every traditional conjuror's act. They're not so much illusionists as disillusionists.

Penn: 'We once did the cups and balls, which is the oldest trick in magic, but we did it with clear plastic cups.' Teller: 'And we did an adapation of the trick where you put someone in a coffin-shaped box and cut it into pieces; ours had a clear plexiglass box. But the tricky thing about showing how tricks are done is that generally the methods involved are so deadly dull. In fact, sometimes we invent new tricks entirely for the purpose of exposing them, just so that the explanations will be interesting enough.'

It isn't just the old guard who are outraged by this policy of baring-the-device, either: in 1991, after they showed television audiences how to work the old con of Three-Card-Monte, a Times Square huckster spat on Penn. But the general public's reaction has been warmer. Since they formed the double-act in 1975 - Teller had been a Latin teacher, Penn was straight out of high school - they have built up a national following for their stage act and their lightning guerilla raids on television - Saturday Night Live, Larry King Live (awkward title, in view of the fact that Teller 'drowned' on air) and a notorious debut on The David Letterman Show. Penn still recalls it gleefully:

'Letterman tends to have a bit of a smug, condescending attitude, so what we did was a standard piece of magic ending with pulling a rabbit out of a hat, and then asked him to critique it, and he was very, very brutal about the whole bit and said that the rabbit out of the hat had been done a zillion times, and he expected something a little more surprising out of us. And we said, 'Oh, you want surprise, Dave?' and we turned the top hat over and dumped a thousand cockroaches on the desk in front of him. He did not know this was going to happen, and he just left, he was off the show.'

Teller: 'But to his great credit, he called our office the next morning and said, 'Come back again and hit me as hard as you like. I hated it, but it was really good television.' '

Others agreed, and the commissions began to flood in. Penn and Teller Go Public, a PBS special, won two Emmys and a Golden Rose at Montreux; their how-to books, Penn and Teller's Cruel Tricks For Dear Friends and Penn and Teller's How to Play With Your Food, were both best-sellers; they hosted an arts series, performed on a rap video with RUN/DMC, and even made a full-length feature with Arthur Penn (no relation: Penn's full name is Penn Fraser Jillette) with the self-explanatory title Penn and Teller Get Killed.

P & T arrived in Britain earlier this week for their first major sortie, but, Paul Daniels, take heed, a full-scale invasion is imminent. Not only are P & T among the acts on Saturday Zoo tonight (in which they will be challenging Jonathan Ross to play Rodent Roulette, a kind of Russian Roulette played with mousetraps); they are also about to make a six-part series for Channel 4, which will, Penn says, 'be very very dense - it'll be the best bits from eight years of American television'.

They're still a little uncertain about how their humour will play over here, though Penn, at least, seems to be catching on to the national sensibility: 'It's like the Inuit having 27 different words for 'snow', the English have a thousand word for masturbation. If it's a verb and you don't understand it, it means 'jerking off'. ' They are reasonably confident that the British will appreciate their brand of jokes, however, since they have always avoided topical or local reference gags in favour of more fundamental kinds of humour: 'We deal with stuff like Trust and Competence and Precision and Lying and Cheating' Penn says, 'not jokes on subjects that divide people, like sex or drugs or politics.'

Their desire to avoid what they call 'allusiveness' also accounts for their choice of stage attire - grey business suits of a Majoresque anonymity. Penn: 'That is ripped off from another magician, Robert Houdin, who Houdini took his name from. Magicians in his day and before always dressed in a Merlin-type outfit, or an Asian-type outfit; and Houdin's breakthrough was to think, wouldn't it be goofy if the magician was to dress exactly like the audience? And that was suit and tails.

'And the wacky thing is that magicians are so dirt-stupid (laughs) that they forget why it was done, and while everyone in the audience changed their dress, the magicians stayed the same, so that this top hat and tails outfit became the sign of the magician. Now, with us, this is the closest thing we can find to being invisible. It's not the political statement of Gilbert and George, of 'This is the uniform of quiet desperation'; it's just that you see everyone dressed in this, and it doesn't give you anything to hold on to.'

Teller: 'Part of what Robert Houdin was doing was helping the audience to identify with him. I think it's much more interesting to watch, say, the needles trick (in which Teller swallows hundreds of needles and then pulls them out neatly threaded) with a fellow who looks like he could be standing in the elevator next to you.'

Showbusiness apart, P & T have one major interest - the debunking of New Age charlatans, just as Houdini used to expose fake mediums: 'Anybody who knows anything about magic soon turns into a debunker. It's a horrendous thing to see people using cheesy tricks to dupe people.' Above all, they insist that even their most gruesome stunts are absolutely safe - 'for us, that is - were you to do it, it would be really dangerous]' So when you see P & T doing one of their greatest hits, the eyeball-razoring routine. . . please don't be tempted to try it at home.

Saturday Zoo: Channel 4, 10pm tonight

(Photograph omitted)