The effect starts with the magician placing a group of cards as a prediction on a crystal clear glass, then a different colored back deck appears on scene.
A part of this different colored back deck gets separated and shuffled by the spectator.
The magician splits this group in four packets with different amounts each, and shuffle each packet once again.
The magician invites the spectator to freely choose one to play with. The chosen group is shuffled by the spectator immediately afterwards.
The first effect happens when the amount of cards in the freely chosen packet by the spectator matches the prediction.
The second effect occurs when not only the amount matches, but also the exact value and exact order of the cards matches the prediction.