Enso by Eric Chien

The audience thinks of a shape. You drip some ink on a blank card and the ink will visually start to move by itself, forming the shape that the spectator is thinking of. The card is then handed out for examination.

This is Enso, one of the most visual moving ink on the market today. Created by Eric Chien and Luo, Enso is only 7mm thick (thickness of 20 cards), you can easily hide the gimmick in a card box or a notebook.