How Magicians Trick Your Brain

The famous Slydini holds an empty box for all to see. It’s not really a box – just four fabric-covered cardboard walls joined together, forming a flexible parallelogram with no bottom or top. However, when the magician puts it on a table, it looks like an ordinary container.

Now he begins to roll large sheets of yellow tissue paper into balls. He claps his hands – SMACK! – crumpling each new ball into a fist, then straightens his arm, wordlessly forcing the audience to look after his closed hand. He opens it, and… the ball is still there. Nothing happened. Eh.

Slydini’s hand closes around the handkerchief, and it begins to meander, slowly and gracefully, like that of a belly dancer. The performance is fascinating. With his free hand, he grabs an imaginary pinch of pixie dust from the box to sprinkle on the other hand. This time he opens his hand to reveal that the handkerchief is missing! Four balls disappear this way. Then, for the finale, Slydini tilts the box forward and shows the impossible: the four balls have mysteriously reappeared inside.

Slydini performed this famous act on The Dick Cavett Show in 1978. It was one of his signature tricks. Despite the conjurer’s incredible showmanship, the sleight of hand only works because your brain can’t multitask.

SPOILER ALERT: The following reveals magical secrets! Stop reading unless you really want to know more.

Slydini’s trick is to create ambiguity and trick yourself into resolving it incorrectly. When he reached the “pixie dust” in the box, he used the same hand motion to drop each ball inside (having previously transferred it between the hands). The pixie dust ploy justified what would otherwise have seemed like unnatural action – a tactic we explained in more detail in an article co-authored with magicians Teller, Apollo Robbins, James Randi, Mac King and Johnny Thompson . Teller refers to this type of action as “movement with a purpose”.

Misdirection works because our brains automatically categorize people’s movements by interpreting their intentions. We see someone push their glasses over the bridge of their nose and assume the glasses have slipped off. But a magician could use the same move to hide something in his mouth. The motion is fundamentally ambiguous, although the action seems clear. It turns out that your brain cannot conceive of an action having two simultaneous goals. So all Slydini had to do was skew your perception to favor one interpretation (hand catching pixie dust) over the other (hand dropping a ball). This is where the magic lies.



Magician Paul Daniels transposed magical ambiguities to the sense of touch with his famous trick called The Powers of Darkness. Here, a volunteer is testing out an ordinary wire coat hanger (top row, left), then an assistant secretly swaps a hanger with a hole (top row, right). With the volunteer’s eyes closed, the magician appears to pass the coat hanger through different parts of the volunteer’s body (bottom row) – although the public can openly see that this is an illusion.

The trick only works because after inspecting the original hanger, the volunteer doesn’t know it was swapped for a gadget and concludes that the solid hanger must have magically passed through his body. He fills the physical void of the hanger in his mind: a practical application of the principle of good continuation [see “The Zig Zag Girl” below] in the tactile domain.



Magician Anthony Barnhart (“Magic Tony”) is also a cognitive scientist at Carthage College. He postulated that some magical acts rely on ambiguous illusions that take advantage of the so-called Gestalt laws of vision. In particular, the Gestalt principle of good continuation asserts that the visual system preferentially organizes aligned segments into continuous objects.

Barnhart suggested that a popular magic trick, the Zig Zag Girl illusion, relies on such ambiguous visual cues. In the standard round (left), an image on the side of the box shows how the woman inside the box should be magically segmented. Without the painted silhouette of the woman (right)the illusion becomes less magical as other bodily contortions seem plausible.

Brian L. Hartfield