#5 Pay attention to their mouth
Rolling the lips back till they have completely vanished is one clue of lying by omission. This could be a sign that someone is hiding information or feelings.
Additionally, studies have shown that those who lie seem to be more prone to pursing their lips in response to delicate questions. Lips pursing could also be a sign that someone is not interested in continuing the current conversation. A liar might also be seen placing their hands over their mouth and lips out of the blue.
When you’re lying, your natural inclination is to hide the source of the lie, your mouth, so that no one can catch you in the act. Since that would be too obvious, people instead cover it up by pinching their noses, which serves the same purpose while giving your hand a plausible excuse for being over your lips.