Poker is the ideal laboratory for this material, because it is the only common activity in which large numbers of people spend years deliberately practicing the suppression of nonverbal leakage, under financial pressure, on camera.
Michael Slepian, Steven Young, Abraham Rutchick and Nalini Ambady took footage from the World Series of Poker and cut it into short silent clips of players placing bets. They then showed the clips to observers with no poker expertise and asked them to judge the quality of the player's hand.
Given clips of the players' faces, observers performed slightly worse than chance — their judgments were mildly misleading. Given clips showing only the arms and hands pushing chips into the pot, they performed better than chance. And given clips of the whole body, performance fell between the two, as though the face were actively interfering.
The face, in the environment where faces are most disciplined, carried negative information. The arms carried real information.
This is Ekman's leakage hierarchy from chapter 31 confirmed in the most demanding possible setting, and the reason it works is motor rather than emotional. What the observers were picking up was the fluency of the betting motion. Confidence produces smooth, decisive, well-timed movement; uncertainty produces hesitation, micro-adjustments, a slightly stilted quality that is hard to describe and easy to see. A player can rehearse a face because the face is a small set of muscles that can be held still. Rehearsing the whole motor character of a movement under real financial stakes is a much larger problem, and one that almost nobody thinks to work on, because everybody is watching faces.
The practitioner literature arrived at a related conclusion decades earlier by observation. Mike Caro's rule — weak means strong, strong means weak — holds that a player who acts uninterested in a pot generally holds a strong hand, and a player performing aggression generally holds a weak one. This is not leakage. It is a second layer on top of it: deliberate counter-signaling by players who know they are being read. Which means at a table of experienced players you are dealing with three things at once — involuntary leakage, suppression of that leakage, and deliberate false signals — and only the first is reliable.
Two lessons transfer well beyond card rooms.
The first is where to look when someone is managing their presentation. In any high-stakes setting where the participants know they are being observed — a boardroom, a witness box, a trading floor, a press conference — the face is the defended channel and is therefore the least informative one. Motor fluency in the incidental actions is not defended: how someone handles a document, pours water, hands over a phone, gets out of a chair.
The second is a warning about the whole enterprise. Slepian's observers beat chance. They did not beat it by much, and this was a domain with a clean, verifiable ground truth, short clips, and a specific well-defined judgment. Take away any of those conditions — as real life does — and the signal is smaller than the noise. Which is the subject of chapter 51.
See Attack: counter-signalling your own tells