During the game, Alice and Bob will pick cards from the deck, identified in which order they are placed in the shuffled deck. When either player wants to see their cards, they will request the corresponding keys from the other player. That player, upon checking that the requesting player is indeed entitled to look at the cards, passes the individual keys for those cards to the other player. The check is to ensure that the player does not try to request keys for cards that do not belong to that player.