The magician gives a card to choose from and it is returned to the deck. These are shuffled by the spectator and placed inside a bag, hat, etc.
The magician shows a rope and puts one end inside, trying to fish out the card chosen by the spectator.
After a few seconds and a lot of effort, he lifts the rope and at the bottom you can see a single card wrapped in a small loop.
It is removed and after the spectator has told the spectator which card has been chosen, it is shown and matches the previous choice.
 
Easy to perform.
 
Can be used with the change bag (sold separately)