Peek a playing card, while it is in the deck, and while the deck is in the box.
– You turn your back
– They shuffle the deck
– They select one card
– They replace it reversed in the deck
– They shuffle again
– You turn to face them, put the cards in the box, and you read their mind.
The peek can be attained immediately, or after deck has been in the box for a couple minutes – it’s up to you.