Balls in Box
The effect: The magician opens a wooden box and shows 3 balls. Take out the 3 balls and vanish one of the ball (ask audience whether they can see the vanishing ball, like "The Emperor's New Clothes"). And then 3 balls are all vanished in his hand! Audience are curious and magician asks if they want to see once again, then he reopens the box, the 3 balls are inside it!