Welcome to Trinity, Dani DaOrtiz’s masterclass on control by making it look like you have absolutely no control. It is the perfect blend of chaos, “free choice,” and psychology.
In Trinity, cards are randomly handed out and shuffled. One person memorizes a card and then all the cards are returned to the table. Now you take another borrowed deck and have the spectators choose 3 random cards to create a number. With only one finger, you then count down to that number in the original deck and miraculously, it’s the spectator’s card.
This is as clean as it gets, if it were a window your finger would be squeaking.