Wes Iseli comes out on stage and hands Alyson a folded sheet of paper containing his “prediction.” He puts it in her pocket. He then pulls out a 50¢ piece and through a series of flips, ends up with one audience member left standing. He then instructs Alyson to pull the “prediction” out of her pocket and read it. Not only does it match the audience member, but she shows the sheet to the audience to read.
The rules of “Fool Us” preclude the use of plants, so the audience member is not in on the trick. The prediction is real—he hands it to Alyson and never touches it again. The coin is a real 50¢ piece—it's not a “gaffed coin” as Penn & Teller guessed.
So how was it done?
It's a method I came up with myself years ago (although I never bothered to keep at it), and it's simple enough: you flip the coin, catch it in one hand. With your finger, you feel the coin and if they are sensitive enough you can determine the orientation of the coin. It's then a matter of “flipping” the coin in your hand (or not) as you slap it down on your wrist.
When I came up with the method, I found that the larger the coin, the easier it was to “feel” the coin and determine heads or tails, but the larger the coin, the harder it would be to hide the “flip” as you slap it on your wrist. An Eisenhower dollar is easy to “feel” but at 1½″ diameter (38mm), it's probably a bit too large to use for the trick. The 50¢ piece however, is large enough to be “easy” to feel and for the audience to see, yet small enough to still hide the “flip” required as you slap it on your wrist.
Yes, it's “simple,” but that's not to say it's “easy.”
So all Wes had to do was spy on the audience prior to coming on stage, write the description of that person on a sheet of paper to hand to Alyson. He then had to make sure all of the flips matched the “prediction” of that particular audience member. And that's it. That's the whole trick.