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Liars often reveal 'loopholes' through their faces, such as smiling and raising their eyebrows to show surprise, according to Canadian scientists' research.

>>>Face monitor to detect liars

According to psychologists, most people can control the lower muscles of the face to chat or eat, but often 'bundle' with more 'stubborn' muscles above the face, leading to the possibility the occurrence of unwanted movements.

Actor Jim Carrey plays the father or lies in
American film Liar Liar. (Photo: Rex Features)

Researchers at the University of British Columbia in Canada discovered four facial muscles that reveal a person's true feelings, such as sin, in stressful situations.

The Telegraph quoted Dr Leanne ten Brinke, who led the study, said: 'Our research shows that facial muscles are not completely controlled. Certain muscles have the ability to "betray" a liar, especially in dramatic situations and emotional outbursts. '

The research team found that liars often leaned on the forehead muscles, such as raising an eyebrow, to show surprise. These people also increased the activity of large cheekbones, located around the mouth, causing them to unintentionally lift their lips to create a smile.

Meanwhile, true people tend to activate the forehead and eyebrow muscles, causing forehead wrinkles and frowning to show real pain. Dr. Brinke said, liars cannot fake such emotional states on their faces.

Although the research results are useful in exposing the liar, Mrs. Brinke warns them not to be 'universal keys' . The scientist stressed: 'Not everyone reveals their true feelings. Moreover, some people are better than others in acting. '