[dsamarin]

With this, you could invent a very unique magic trick where your spectator well-shuffles a deck of cards, then you can secretly swap your deck with one of the decks from your collection to reveal that yours was shuffled in the exact same way.

[vunderba]

This is a relatively well known technique in card manipulations known as a "cold deck". There are many variations of it involving probabilistic but not entirely deterministic forces that lead to a branching path to a different cold deck.