If it is, they can use the sleight of hand and take the next card.
Dealers can also mark the cards with little bumps that they can feel while dealing.
By marking the face cards, they have an edge on the player. Dealers have also been known to pretend to shuffle the deck after picking up the cards in an alternating order. They can also deal from the bottom of deck. If it is, they can use the sleight of hand and take the next card. By marking the face cards, they have an edge on the player.