I was doing the biddle trick, and I did the most bone-headed thing possible... I forgot what their freakin' card was. I was so pleased with the convincing controlled shuffle I did, that when I did the biddle move their card flew right by me, I spaced out, and forgot what it was. A classic case of biddling under the influence.
No sweat. Some quick thinking-on-my-feet saved the trick. I hold the cards in my card, and make two wrong guesses on purpose. I act disappointed and say, "Well, what was your card?" They tell me "Seven of clubs." I hold out a card showing it's back and say, "Oh, the seven of clubs here, that was my next guess! Well I can't do that trick very well, but here's a trick I can do. Take your seven of clubs (show back of indifferent card) and look..." (snap--it vanishes) "Look in the deck you're holding, right in the middle, there it is, face up."
In the end the effect was really not much different from the normal Biddle trick, and nobody guessed for a second that anything had gone wrong at all. A good example of where you should not panic just because things didn't go exactly by the script.