Card of Gods by Dai Vernon

Any deck is well shuffled by a spectator who then cuts off about a third of the cards. He is asked to look them over and finally settle his mind upon any one card in the packet lie is holding.

You now take the packet, fan it, and appear to be trying to locate the thought-of card.
Actually you look for two spot cards of like value, preferably from 6 to 10. These are kept together and are moved about in the fan, which is held face towards you, so that the second of the two cards will occupy its own number from the top of the packet. Thus, if you use two "nines," one should be placed eighth and the other ninth from the top; if two "eights," one should be seventh and the other eighth.

Professing failure in your search, you say that you'll deal the cards into a face up pile, and ask the spectator to watch for his chosen card and note its position in the pile. The spectator thus watches for his card to remember the number it will fall at, while you take the opportunity of noting the total number of cards in the pile.

You now replace the packet of cards just counted face down on top of the deck, and proceed to shuffle the entire deck in the following manner. It is extremely simple and there is little to forget. Undercut ;bout half of the pack, slip one card, injogging it, and shuffle off the rest. Cut under the jogged card, shuffle run the number of cards you stacked, injogging the last, and throw the rest on top. Square the deck somewhat and cut below the jogged card, placing the two piles thus cut onto the table. Remember which packet represents the top half of the cut, and which packet represents the bottom of the cut.

Now tell the spectator that strange as it seems, and impossible as it sounds, you are sure he has the intuition necessary to locate his own chosen card. Tell him to pick up one of the two piles, warning him that unless he picks the correct one the test must fail. However, you insist that you are certain he'll choose the correct heap.
You are perfectly safe regardless of which heap he selects. If he indicates the pile
representing the top half of the cut, you merely turn it face up revealing one of your
stacked pair as the bottom card. If he picks the other heap, you turn over its top card only which is the other one the set pair. Saying that the card thus revealed will find his thought of, you ask him what number his card occupied in the original pile. It may have been seventh, tenth, fifteenth, etc.

Using this number and the value of the card showing, you subtract the smaller number from the larger, count to the resulting figure in one of the piles, and the card at the number proves to be the one of which he is thinking.
The designation of the pile in which the counting is done is arrived at in the following way. If the number given by the spectator is less. than the value of the card turned up-the counting is done in the pile representing the lower half of the cut. If the number given by the spectator is higher than the value of the card turned up-then the counting is done in the pile representing the top half of the cut.

Telling the spectator that he will always be correct in his pile selection is important, and has much to do with the impressiveness of the feat. The turned up card either finds the thought-of-card in the opposite pile, or in its own, and this is logical in each case. If in the top pile (which has been turned over completely and face up) the packet is turned face down for the counting. If in the bottom pile( the top card of which is the only one turned face up) the top card is turned face down again before the counting is done.