Pinocchio made lie detection easy.
Steven Lubet’s "Dicta" column in the March 2007 issue of The American Lawyer highlights the conceit, common among judges, that watching someone’s face allows them to determine the witness’s truthfulness. He mentions that even professional lie detectors (including CIA agents and trial lawyers) fail in their craft at least half the time. Who does better? Poker players, who over time observe deviations from other players’ baseline behavior. Ah.
One’s face tells the least about prevarication. Hence "poker face".
Which body part conveys the most reliable information? Your feet. Interesting.