I used to do this amazing card trick. I'd fan a deck and ask the victim to "pick a card, any card." The person would pick a card and I'd say, e.g., "six of diamonds." Fifty-one times out of fifty-two the victim would say I was wrong, to which I'd reply, "well, it works about once out of every fifty-two times." One time, after saying "three of clubs" the person showed the card to be the four of clubs. He was so amazed that he had me do it four more times with predictable results. He never did get the idea.