Does anger mean honesty?
A fairly robust finding in the deception literature is that lie-tellers show more negative emotion than truth-tellers. Ekman (1985), however, has reasoned that a specific type of negative emotion – anger – is especially difficult to feign and therefore should be more prevalent in truth-tellers who are falsely accused of a transgression than in lie-tellers who are guilty. To our knowledge, Ekman’s prediction has not yet been empirically tested. By comparing the verbal and nonverbal cues associated with truths and lies across a number of lie-eliciting situations, we demonstrate that truth-tellers accused of a wrongdoing do show more anger, both verbally and nonverbally, than lie-tellers accused of the same act, but only in situations where students choose to commit a transgression (or not) and actually believe themselves to be in trouble. Results underlie the importance of taking into consideration the type of lie being told in order to accurately predict deceptive cues.
Source: “Anger as a cue to truthfulness” from Journal of Experimental Social Psychology, Volume 46, Issue 4, July 2010, Pages 680-683
The study above references the work of Paul Ekman, which is fascinating and, if performed by someone well trained, can be pretty effective.