The Mossad Reappearing Ink Pen from ThinkGeek “has ink that disappears when you apply heat and reappears when you apply cold — gel ink disappears at 140F and reappears at 15F.” Video after the break.

There is no better way to pass secret notes than the Mossad Reappearing Ink Pen. And because it’s a gel pen, you don’t need to press hard (so you won’t leave any telltale indentations on the paper).

[via ThinkGeek]