You reveal a chosen card from behind your back without looking.
Turn your back to the audience. Tell volunteer to think of a number between 1 and 10. Then ask him/her to shuffle the pack and get him/her to count down to the number they thought of and make a note of the card but leave it in the same position.
After he/she has done this, turn around and take the pack placing it behind your back then count off 19 cards and as you do so reverse their order replacing them on the top of the pack. As you do this, say that you will put the card at number 20.
Finally, bring the pack from behind your back and ask the spectator which number he thought of — for example if it was a five then begin your count with in this example 6 dealing the cards one at a time. When you reach 20, get the spectator to name his card and when you turn it over, to his amazement, it is his card.