Then There Were Four

A spectator holds one sponge cube in his closed hand, the magician touches his hand with a magic wand and the sponge multiplies to two. The spectator then taps the two with the magic wand and they multiply to three. Finally the three cubes are plainly placed in the spectators hand, and the magician asks "Would you believe there are four now?". He taps the hand with the magic wand and the three sponge cubes magically transform into figure FOUR. Very easy to do, packs small, plays big.