702.5. Looking at Extra Cards [Warning]: A player takes an action that enables them to see the faces of cards they are not entitled to see.
702.5.a. Players are not entitled to see cards that are private (to another player) or secret.
702.5.b. Cards in a deck are considered to be in that deck unless and until they touch cards in another private or secret group. If that happens, the error is instead a Secret Card Error.
702.5.c. Remedies:
702.5.c.1. If the cards remain in a single deck, shuffle the deck appropriately to remove the information advantage.