Show your pack of gum and make a scribble on it with your Marker. You can touch and rub it, it is real ink. Shake the gum and visually the ink morphs into any drawing or any writing. You can also make the ink vanish and reappear anywhere you like.

It's simple and very practical. It can be examined before and after.

No threads or magnets involved. You can make it in a seconds.