Zig Zag Card
As you tell the story of how magicians are notorious for cutting their assistants in half, you show an ordinary playing card and an interesting looking card frame. The playing card is placed inside the frame and you literally slide over the middle of the card severing it from the rest of the card. You can show the frame from all sides as everyone gazes at this mystery. Then, you slide the middle back into place and remove the card and show no harm has been brought to the card as it is completely intact!