Two cards are placed face up on the table. You now show four misprinted cards that have backs on both sides--except for one, which has a back and a blank face. "I'll put this aside for now as this can be a rather dangerous card...I'll explain later," you say. This leaves you with three cards--backs on both sides, which you show once more. You now add the first selection to the packet and suddenly all the cards print with faces of the selection! You repeat this with the second selection to erase all the cards to print to duplicates of this card! Finally you pick up the "Dangerous Card" with the blank face. "This, " you state, "is an eraser!" You now prove this to be so because, suddenly, all the cards turn blank!