Mentalex?

After disgusting your audience with a convincing discourse on mind control, you borrow two stiff hats and place down up on two chairs about I-1/2 yards apart. Stepping amongst the multitude you request several to select the card you want them to, but you have deceived them just the same because you don't force a card! The cards are returned and you do the shuffling so that there will be no tricky work. Placing deck in one lid, you remove cards singly, backs towards audience and transfer to other hat. One of the selectors is asked to call stop at any time when a card is half way across and on naming it is turned around and of course, as usual, you are right. Repeat with the others if they have not left.

Because of the bewildering and intricate sleights necessary for the accomplishment of this problem I use a three kind force deck to save time in practicing. As there are at least 15 duplicates of each the spectator is sure to call stop before very many have passed by because he wants to see the other acts before he has to go. They really think it is mind control and that is why they flock around you after the show and say, "Did you take a course?" "Were You always good at it?" "Did you get it out of Popular Science or Science and invention magazine?"

(Annemann - Buried Treasure)