If you think you can spot a liar by their shifty gaze and hesitant manner, you may need to think again.
The most untruthful people are likely to look you straight in the eye and give confident, thought-out replies, research claims.
They are also likely to grimace, make excessive hand gestures and use fill words such as "um" and "err", claim experts from the University of Michigan.
Researchers have developed the first lie-detecting software, based on video footage of 120 court cases in the United States, that can spot someone who is lying 75 per cent of the time.
Humans spot a liar just 50 per cent of the time.
Psychologists and law enforcers previously believed liars tend to give hesitant answers and often avoid eye contact. But such results come from studies based on lab experiments.
Dr Rada Mihalcea, a professor of computer science and engineering who leads the Michigan project, said: "In laboratory experiments, it's difficult to create a setting that motivates people to truly lie. The stakes are not high enough. But in the real world, there is true motivation to deceive."
The team used video footage from defendants and witnesses in hearings such as murder trials, transcribing their words and counting gestures.
In the clips, the subject was deemed to be lying or telling the truth based on how their testimony aligned with the trial verdicts. The team then fed the data into a computer, which used an algorithm to look for the most common patterns of liars.
The software could identify a liar on three out of four occasions, based on several "tells" - slips in behaviour or speech. People who lied were three times more likely to scowl or grimace rather than keep a relaxed face.
Liars were also more likely to look directly at the questioner, gesture with the hands and use language to distance themselves from the proceedings - by saying "he" or "she" not "I" and "we".
"People are poor lie detectors," Mihalcea said. "There are clues that humans give naturally when they are being deceptive, but we're not paying close enough attention to pick them up. We're not counting how many times a person says 'I' or looks up. We're focusing on a higher level of communication."
The team are hoping to make the test more accurate by adding in physiological signs such as heart rate, respiration rate and fluctuations in body temperature, which can be picked up remotely.
People are known to sweat more when they lie, and their breathing increases.
The research was presented at the International Conference on Multimodal Interaction and is published in the 2015 conference proceedings.Telegraph Group Ltd