The magician shows a card with a hole in it. He grabs the hole and stretches it. After a moment the hole morphs back to its original shape. But that is not all. The magician slowly peels the hole from the card - the hole becomes a sticker and the card is solid, restored to its normal state.
Both sides of the card can be shown (from some distance). The hole just disappears. Additional supplies may be needed in order to perform the effect. Requires arts and crafts to prepare the gimmick.