We measured the continuous bodily motion of participants as they lied to experimenters. These lies were spontaneous rather than elicited, and occurred for different motivations. In one situation, participants were given the opportunity to lie about their performance on a maths test in order to win money. In another, they witnessed one experimenter accidentally break a laptop. When asked what had happened, participants were motivated to lie and deny any knowledge. Across these situations, participants lied 61% of the time, allowing us to contrast the body movements of liars with truth tellers as they answered neutral and critical questions. Those who lied had significantly reduced bodily motion. In one case this motion appeared before the experimenter had even asked the critical question. We conclude that a persons bodily dynamics can be indicative of their cognitive and effective states, even when they would rather conceal them.