Photograph by Nick Veasey

The final moments of a poker hand are agonizing. The chips are in the pot; your opponent just raised your last bet. Call or fold? What are you going to do? Your opponent, a regular at this Friday night game, looks around the room. He fixes his hair. And then it happens. “So, Johnny, you see the Lakers game last night?” he says. That’s all you need: He’s bluffing. You know this guy. If he were holding a winning hand, he’d feign nervousness. You bet the bank.

In the gambling lexicon what you’ve just witnessed is a “tell.” As I describe in my recent book Poker Nation, many poker players have a subconscious tick or mannerism that gives their cards away. It could be the way they stack their chips. Their smile. Some people’s hands shake when they’re holding a full house, others when they’re bluffing. Play against someone often enough and you can start using his tells to your advantage. If you don’t, he’ll start using yours.

Tells aren’t limited to poker. Body language is an efficient lie detector in any situation. Pay attention to eye contact. Rare is the unfaithful spouse who can deny infidelity while looking into his partner’s eyes. Posture is another tip-off. When someone bends the truth, he often stands ramrod straight in an attempt to look as respectable as possible. But there is perhaps no better tell than the human voice. A guilty man will overemphasize the specific word necessary for the lie: “I didn’t do it.”

Master these tells and the game of poker, and of life, will grow more profitable.