The magician announces that he is going to perform a mind-tuning experiment using two spectators.
He hands the giant half-cards to one spectator. With his back turned, he indicates that the cards should be shuffled and that a small pile should be given to the other spectator taking part in the experiment.
Each of the spectators should count and memorize, in silence, the number of half-cards in the pile in their hands. Once this is done, they must put their cards together and shuffle them again.
The magician points out that it is impossible to know how many half-cards each of the elements had. He now takes the pile and starts passing the half-cards to the first spectator, asking them to memorize the value of the half-card corresponding to the number of cards in their pile after the initial division. For example, if the spectator had 5 cards in their hand, they should remember the value of the fifth half-card that the magician is passing in front of them. It should be noted that spectators should not announce it.
Once the count is complete, repeat the procedure with the second spectator.
When you've finished, hand the half-cards to the first spectator and ask them to remove the half-card they've memorized and place it face down on the table. Then ask the second spectator to do exactly the same.
We now have two half cards on the table face down.
Once the two half-cards are turned over, it's clear that they match up to form a complete card.