SINK HOLE is a gimmick that allows you to penetrate a Sharpie right into the face of the card visually.
Imagine this. You ask your spectator to select a card. After that, you introduce a Sharpie and stab it into the card. The Sharpie now penetrates the card. You then ask your spectator to please pull out the Sharpie, and they see the hole heal by itself visually. Looks amazing!