I suppose the main thing to recommend this effect is the shock value of the naked woman at the end... or maybe that is the main thing to not recommend the trick? It all depends on your style and the audiences you work for. If you have a loose adult audience, like a table-full of twenty something guys having a boys-night-out, then this is one of those simple tricks that gets a reaction way out of proportion to the method and effect. (If you have a table-full of nuns, trying to have a quiet evening meal, you should skip this one.)
The effect is simple, a la the classic Mental Choice effect. (But with a different method.) Show three ESP cards, the size of business cards and printed on something similar to business card stock. (I laminated my personal set of cards so they would last forever. You might wish to do the same.) The three symbols are placed faceup on the table, and the spectator is given a magic crystal to hold. The crystal, you explain, will read his mind and reveal the quality of his mental processes. The spectator is told to squeeze the crystal, then to put the crystal down and pick up two cards. He picks up the Circle and the Star (for example). He is now told to look at the crystal and to place one of the cards under the crystal. He places the Star under it. The magi takes the other card from him, and shows the backs of the Circle and Waves -- they say "Normal" on the back. "You had two chances to choose these normal cards, but the crystal could see your true thoughts and has forced you to reveal them." The card under the crystal is turned over, and it shows a topless young woman with the caption "You have a one track mind."
The selection process described above is slightly enhanced from what is described in the instructions. But if you are familiar with equivoque techniques, you will understand how the use of the crystal adds some logic to the process when you need to do something illogical. :-)
Comes with the three cards, crystal and instructions. Brand new, unused, even though the stock is almost 25 years old.