Martin Lewis' Big Switch

You present a deck of cards and tell the audience that you have made a prediction and it is in your inside coat pocket. You proceed to let a spectator choose a card and then show you have predicted it by removing from your pocket a Jumbo Eight of Spades. The spectator protests that this is incorrect, so you ask for the name of the card that they chose. They say, "Queen of Hearts." You say, "In that case, I must perform a switch." You turn the card around and fixed to the back is a wall switch! You solemnly flip the switch, and when you turn the card around again, it has now switched to the correct card, the Queen of Hearts!