"Is he lying?" Odds are, you'll never know. Although people have been communicating with one another for tens of thousands of years, more than 3 decades of psychological research have found that most individuals are abysmally poor lie detectors. In the only worldwide study of its kind, scientists asked more than 2,000 people from nearly 60 countries, "How can you tell when people are lying?" From Botswana to Belgium, the number-one answer was the same: Liars avert their gaze.

"This is ... the most prevalent stereotype about deception in the world," says Charles Bond of Texas Christian University in Fort Worth, who led the research project. And yet gaze aversion, like other commonly held stereotypes about liars, isn't correlated with lying at all, studies have shown. Liars don't shift around or touch their noses or clear their throats any more than truth tellers do.

For decades, psychologists have done laboratory experiments in an attempt to describe differences between the behavior of liars and of people telling the truth. Some researchers, however, are now moving away from those controlled conditions and are inching closer to understanding liars in the real world. The researchers are examining whether several behaviors that have emerged as deception signals in lab tests are associated with real-life, high-stake lies. The psychologists are also testing how well professional sleuths, such as police and judges, can detect deceptions.

One thing, however, is certain: There is no unique telltale signal for a fib. Pinocchio's nose just doesn't exist, and that makes liars difficult to spot.

LAB LIES By studying large groups of participants, researchers have identified certain general behaviors that liars are more likely to exhibit than are people telling the truth. Fibbers tend to move their arms, hands, and fingers less and blink less than people telling the truth do, and liars' voices can become more tense or high-pitched. The extra effort needed to remember what they've already said and to keep their stories consistent may cause liars to restrain their movements and fill their speech with pauses. People shading the truth tend to make fewer speech errors than truth tellers do, and they rarely backtrack to fill in forgotten or incorrect details.

"Their stories are too good to be true," says Bella DePaulo of the University of California, Santa Barbara, who has written several reviews of the field of deception research.

Liars may also feel fear and guilt or delight at fooling people. Such emotions can trigger a change in facial expression so brief that most observers never notice. Paul Ekman, a retired psychologist from the University of California, San Francisco, terms these split-second phenomena "microexpressions." He says these emotional clues are as important as gestures, voice, and speech patterns in uncovering deceitfulness.

But not all liars display these signals, and one can't conclude people are lying because they don't move their arms or pause while telling their stories. These could be natural behaviors for them, not signs of lying. "They are statistically reliable indicators of deception," says Timothy Levine of Michigan State University in East Lansing, but that doesn't mean they're helpful in one-on-one encounters.

People don't seem to be very good at spotting deception signals. On average, over hundreds of laboratory studies, participants distinguish correctly between truths and lies only about 55 percent of the time. This success rate holds for groups as diverse as students and police officers. "Human accuracy is really just barely better than chance," says DePaulo.

Some researchers think, however, that the design of the laboratory studies is responsible for the poor rates of lie detection. "People are very good liars when nothing is at stake," says Aldert Vrij of the University of Portsmouth in England. "But a lab setting is not real life. …