File photo. Picture: cinnamon_girl, Flickr

London - If you want to spot a liar, look at the way their mouth curls when they smile.

Although nervous fidgeting is commonly associated with fibbers, this is not a foolproof way of spotting when someone is telling a whopper, according to researchers.

They said a genuine person smiles with their eyes, while fake smiles are only in the mouth.

Liars also sometimes show “a smile of contempt”, with one side of the mouth slightly up-turned, indicating they are getting away with something.

But to really nail a cheat, the key is to observe someone over time, experts said, because you notice changes in behaviour that give the game away.

David Matsumoto, a San Francisco State University professor of psychology, said the skill of foiling fibbers can be developed through practice. The key is to create “a baseline” of an individual’s behaviour, a sense of what people look and talk like when their guard is down and they are telling the truth.

Pamela Meyer, CEO of private firm Calibrate, which trains people and companies about how to spot deception, said once a baseline is established, you should ask open-ended questions and look for cues and changes in verbal and physical behaviour.

For example, liars may split hairs, decline to answer, change the subject or tone, protest a question, even put up their hands while objecting, Meyer said.

According to Professor Matsumoto, it is also a good idea to look for additional information to prove someone is telling lies.

For example, police will ask for a disjointed or backward timeline of someone they are interrogating, he said. This is because fake memories are made in chronological order so they are harder to call up backward.

Matsumoto said it was a myth that fidgeting is a sign of lying because many people naturally fidget or freeze when they are under pressure.

Instead he said the key is to look for a change in behaviour, not a specific action, and to look at the face. “Research has shown that the bulk of messages in any action is communicated nonverbally,” Matsumoto said.

Children learn to lie at an average of around three years old, often when they realise that other people don’t know what they are thinking, according to Kang Lee, a professor at the University of Toronto.

He has done extensive research on children and lying, including setting up an experiment in a video-monitored room to see if he could catch them fibbing about peeking at a toy when an adult left the room.

At age two, only 30 percent lie, Lee said. At age three, half do. By five or six, 90 percent of the children lie and Professor Lee said he worries about the 10 percent who don’t because lying is a universal trait.

Daily Mail