If you've ever sold used cars or peddled vacuum sweepers door-to-door, you probably know this from experience: Researchers have found that an attractive physical appearance and positive nonverbal cues, like eye contact, smiling and a pleasant tone of voice, may have as much or more of an influence upon us than the actual words that the person is saying. In fact, someone who is skilled at nonverbal messaging can actually foster what communication experts call a halo effect. That is, if we think that a person looks good, we assume that he or she is intelligent or capable as well. That's a big help in fostering credibility [source: Eadie]. But just as a salesperson can learn to project a convincing demeanor, a swindler or a dishonest politician can practice the same tricks.
However, other nonverbal cues provide useful information for evaluating whether someone is telling the truth or a lie. Researchers who've studied the questioning of criminal suspects, for example, note that even highly motivated, skillful liars have a tendency to "leak" nonverbal clues to their deception in the course of a long interview, because of the difficulty of managing facial expressions, physical carriage, and tone of voice over time. The trick is to watch for those tiny flaws in the subject's demeanor to emerge.
When making an untrue statement, for example, a person may flash a "microexpression"-- a frown, perhaps, or a grimace -- that reflects his or her true emotions, but clashes with what the person is saying. Since some of this microexpressions may happen as quickly as the blink of an eye, the easiest way to detect them is by replaying a video. But it is possible to do it in a real-time conversation as well. U.S. Coast Guard investigators trained in spotting such leakage, for example, have been able to spot such clues about 80 percent of the time [source: Matsumoto, et al.].