It's Only One
You state that for your next trick you will need three balls. Suddenly one appears in your right hand and two in your left. You then allow the audience a chance to examine these. Then the two balls are placed into your spectators hand and the third vanishes.
You now place two balls in your hand, one in your pocket. Opening your hand, there are three balls! Once more, you put two in your left hand, one in your pocket and ask the spectator how many balls are in your hand. Regardless of the guess, he answers, "But I only have one in my hand-" then opens his hand to show the number 1!
Comes complete with all the necessary sponges + Bonus rutine af Frank Zak