Tell your spectator that in a moment you want them to think of one of cards you are going to show them, but also tell them that you are going to try and influence their decision. In front of your spectator lay down (in this order from their left to their right) the King of Hearts, the Seven of Clubs, the Ace of Diamonds, the Four of Hearts, and the Nine of Diamonds. Ask him to mentally choose any card, and lock it into their mind. You’ll find that 80% of the time, they will choose the Four of Hearts. Try it!
The key to this one is dropping just a hint that you might try to influence their decision. Once they hear that, they’ll eliminate the Ace of Diamonds as being too obvious as a choice. They’ll mentally eliminate the Seven of Clubs since it’s the only black card. They’ll eliminate the King of Hearts as the only face card and people usually eliminate the Nine of Diamonds since it’s on the end.