As we have said, most people cannot consciously distinguish a fake smile from a sincere smile. We are quite satisfied when the interlocutor smiles at us, even if not with all his heart. Since the smile immediately disarms, many mistakenly believe that it is the favorite means of the liars. Studies conducted by Paul Ekman have shown that when people intentionally lie, they smile much less often than they normally would. This applies especially to men. According to Ekman, this happens because the liars understand that most people associate smiles with deceit and consciously try to smile less often. A false smile appears faster sincere, lasts longer, as if a liar put on a mask and is not in a hurry to remove it.
A fake smile is more pronounced in one side of the face, although both hemispheres of the brain work on it. That part of the cerebral cortex, which is responsible for facial expression, is located in the right hemisphere. It sends signals mainly to the left side of the body. As a result, fake facial expressions on the left are more pronounced than on the right. During a sincere smile, both hemispheres of the brain act on both sides of the face, and the smile is symmetrical.
When a person lies, his smile is much more pronounced on the left side than on the right.

Smugglers smile less often

In 1986, we advised Australian customs. We were offered to participate in a program to detect smuggling imported into Australia. Until that time, customs officers believed that people, being under pressure and speaking a lie, smile much more often. Our analysis of videos of people who deliberately speak untruths proved the opposite. When a person is deceiving, he smiles much less often or does not smile at all, regardless of cultural traditions. He who is not involved in anything and speaks the truth, smiles more often because he is confident in his honesty. Since the smile demonstrates obedience and submission, innocent people immediately try to demonstrate this to their accusers. Cheaters reduce the number of smiles and try to suppress other signals of the body language. The same thing happens when a police car stops near you at a traffic light. Even if you did not break the law, the mere presence of the police is enough to make you feel guilty and start smiling. Thus, it can be said that a smile can be imitated, and therefore, it should always be considered in the context of the current situation.