Observing the dealer's body language and expressions to determine his hand of cards.

Playing the game by observing other players (or the dealer in Blackjack) and trying to detect subtle body language that may give away vital information.

This refers to a playerâ€(tm)s carefully observing a dealerâ€(tm)s facial expressions and general manner in order to determine what heâ€(tm)s got in his hand.