It's Only One

The magician shows his hands to be empty. For his next effect, he needs three sponge balls. Suddenly one appears in his right hand and two appear in his left hand, the third in his pocket, asking the spectator how many he has in his hand, they answer "two". He says, "I have only one in my hand", whereupon he opens his hand and out pops a large cut out of the number "1".