One of the first tricks in Penn and Teller's Las Vegas show begins when Teller—the short, quiet one—strolls onstage with a lit cigarette, inhales, drops it to the floor, and stamps it out. Then he takes another cigarette from his suit pocket and lights it.

No magic there, right? But then Teller pivots so the audience can see him from the other side. He goes through the same set of motions, except this time everything is different: Much of what just transpired, the audience now perceives, was a charade, a carefully orchestrated stack of lies. He doesn't stamp out the first cigarette—he palms it, then puts it in his ear. There is no second cigarette; it's a pencil stub. The smoke from the first butt is real, but the lighter used on the pencil is actually a flashlight. Yet the illusion is executed so perfectly that every step looks real, even when you're shown that it is not.

Penn and Teller demonstrate the seven basic principles of magic.

The trick is called Looks Simple, and the point is that even a puff on a cigarette, closely examined, can disintegrate into smoke and mirrors. "People take reality for granted," Teller says shortly before stepping onstage. "Reality seems so simple. We just open our eyes and there it is. But that doesn't mean it is simple."

For Teller (that's his full legal name), magic is more than entertainment. He wants his tricks to reveal the everyday fraud of perception so that people become aware of the tension between what is and what seems to be. Our brains don't see everything—the world is too big, too full of stimuli. So the brain takes shortcuts, constructing a picture of reality with relatively simple algorithms for what things are supposed to look like. Magicians capitalize on those rules. "Every time you perform a magic trick, you're engaging in experimental psychology," Teller says. "If the audience asks, 'How the hell did he do that?' then the experiment was successful. I've exploited the efficiencies of your mind."

Now that on-the-job experimentation has taken an academic turn. A couple of years ago, Teller joined a coterie of illusionists and tricksters recruited by Stephen Macknik and Susana Martinez-Conde, researchers at the Barrow Neurological Institute in Phoenix, Arizona, to look at the neuroscience of magic. Last summer, that work culminated in an article for the journal Nature Reviews Neuroscience called "Attention and Awareness in Stage Magic." Teller was one of the coauthors, and its publication was a signal event in a field some researchers are calling magicology, the mining of stage illusions for insights into brain function.

"Tricks work only because magicians know, at an intuitive level, how we look at the world," says Macknik, lead author of the paper. "Even when we know we're going to be tricked, we still can't see it, which suggests that magicians are fooling the mind at a very deep level." By reverse-engineering these deceptions, Macknik hopes to illuminate the mental loopholes that make us see a woman get sawed in half or a rabbit appear out of thin air even when we know such stuff is impossible. "Magicians were taking advantage of these cognitive illusions long before any scientist identified them," Martinez-Conde says.

For sleight-of-hand master Teller, magic is a form of experimental psychology. Photo: Carlos Serrao

Penn and Teller are an n of 1 in American culture: avant-garde artists who perform for the Vegas masses, skeptical philosophers who somehow got a cable TV show. For the past 25 years, they've played the same characters onstage. Teller is the silent, impish illusionist—"People are always surprised that I can speak," he says—while Penn is the hyperkinetic impresario, juggling knives, teasing the audience, and swallowing fire. These personae reflect the men's offstage personalities. Penn Jillette is 6'7", with a mane of curly black hair. When he walks, he pounds the floor like a clown in oversize shoes—not surprising, since he graduated from the Ringling Bros. and Barnum & Bailey Clown College. Teller is nearly a foot shorter and dresses in dapper three-piece suits. He has an eerie grace, as if he can move without displacing air.

The two started performing together in 1975, playing Philadelphia street corners and Renaissance festivals. Along with a third artist, they called themselves the Asparagus Valley Cultural Society, an absurdist act that mixed knife-juggling with "unusual and disgusting" classical music. They were not especially popular. "I always assumed I'd spend my life happily performing in artsy-fartsy little theaters," Teller says.

After their first Renaissance gig, where Teller performed in tights and Penn in leather, they were headed back to New Jersey. To kill some time in a diner, Teller was practicing his version of Cups and Balls, a classic sleight-of-hand trick popularized by ancient Roman conjurers. It involves a series of "vanishes" and "transpositions" as the balls appear and disappear underneath the cups. Teller hadn't brought any props, so he used wadded-up napkins and clear water glasses.

Penn & Teller demonstrate their version of Cups and Balls.

Somehow, this made the trick even better. Although it was now possible to follow the crumpled napkins as Teller variously palmed them, squished them, and moved them from cup to cup, the illusion persisted. "The eye could see the moves, but the mind could not comprehend them," he says. "Giving the trick away gave nothing away, because you still couldn't grasp it." They eventually worked this version of Cups and Balls into their show, and audiences loved it. But the magic community—whose cardinal rule is "Don't tell 'em how it's done"—reacted with outrage and even threats of physical violence. Penn and Teller were exposing an ancient secret! Two arty geeks were destroying the mystery!

All that criticism got press attention, which made people want to see Penn and Teller even more. Before long, they were performing Cups and Balls on Letterman. The trick became a centerpiece of their first off-Broadway show. "It was so liberating to be able to treat the audience like intelligent adults," Teller says. Instead of engaging in the "usual hocus-pocus clichés," the clear cups forced the crowd to confront the real source of the illusion: the hard-wired limitations of their own brains. Because people were literally incapable of perceiving the sleight of hand—Teller's fingers just moved too fast—it didn't matter that the glasses were transparent.

Penn and Teller still perform Cups and Balls—it's one of the few old bits in their current Vegas show. Several of their other pieces take a more direct cue from research on perception. In the Cowboy trick, an individual from the crowd is given a video camera; Penn says he's going to make a tiny plastic cow disappear from his hand, and he asks the audience member to film the vanish as the feed is projected onto a large screen for the rest of the room. While the mark focuses on Penn's flamboyant hand gestures—and the impertinently nonvanishing cow—Teller rearranges the entire stage in plain view. The audience cracks up; even when the poor sap looks up from the viewfinder, he fails to notice that anything is different.

Richard Wiseman demonstrates the Colour Changing Card Trick.

"The idea for this trick came straight from science," Teller says. "We thought it would be fun to show people how bad they are at noticing stuff." Called change blindness, the phenomenon is illustrated in a video (on YouTube) that inspired the duo. Shot in 2007 by British psychologist Richard Wiseman, it ostensibly documents a simple card trick—the backs of the cards in a deck are magically transformed from blue to red. But during the course of the video, Wiseman's shirt, his assistant's shirt, the tablecloth, and the backdrop all change color, too. Most viewers watch the card trick unspool and miss the other alterations. Attention, it turns out, is like a spotlight. When it's focused on something, we become oblivious to even obvious changes outside its narrow beam. What magicians do, essentially, is misdirect—pivot that spotlight toward the wrong place at the right time.