Mentally simple - ingeniously simple.

Five different ESP cards are placed on a stand, leaning against the back wall. A spectator mentally selects one (i.e., without touching it). No one in the room—except the spectator—knows which card they have chosen.

Now you take these five cards, then look penetratingly at the participant and place one of the cards behind the stud wall; put the others away.

Your spectator now calls out the card you're thinking of. At the same time, you take the backing card from the stand and throw it onto the table. Your audience will be looking at the back of the card you placed there.

The card is turned over - it bears the symbol the spectator thought of!!!