Transpo Cards

The magician shows a small wallet that has two cards clearly visible inside: a 7 of clubs, and a 7 of diamonds. He takes out the 7 of diamonds, and puts it face up on the table. He then takes the 7 of clubs and puts it face down onto the first card. A magical gesture, and the printed face of the 7 of clubs disappears leaving the card blank, and ends up…on the back of the 7 of diamonds!