You present to your spectator the first ever soundproof playing card box. To show that it is soundproof you place a coin inside, close the box and give the box a shake. Sure enough they cannot hear the coin.
THEN you tell them that the box is NOT soundproof, and that the only reason they couldn't hear the coin inside, is because you told them that they wouldn't be able to. To show them that this is true, you give the box another shake and sure enough this time they can hear the coin inside.
NO palming,No adhesives, hands can be shown EMPTY throughout, EASY to master.