The Crag is a truly fascinating effect built through continuous surprises and twists.
The magician has a blue deck in his hands and asks the spectator to touch four cards freely. After the spectator has chosen four cards, the magician shows him which cards they are. The spectator names one of the four cards and incredibly it is the only card that has a different colored back. At this point the twists begin because the magician shows that even if the spectator had chosen another card, this would also have had a different back. So the effect continues by showing that the spectator's cards change their backs one after the other and in the end they all have a different color: none of the chosen cards remained blue. Finally the great Finale.
The spectator has touched the only existing cards in the deck because all the others are blank.

No Glue
No Sticky stuff
No Rough and smooth