Ex-FBI agent Joe Navarro explain in his book What everybody is saying that nonverbal cues put out by the limbic mind are paramount to detecting deception. He says that it is the displays of comfort versus discomfort that tells body language readers when someone is telling the truth or lying. When people lie they experience discomfort and “guilty knowledge” which leaks through the body due to the fear response, but when people tell the truth, they “have no worries.” This approach says that a person uses more emphatic gestures with their hands and arms when they tell the truth, but when they lie they tend to freeze up and lock themselves down. By extension, we should be careful not to grill someone for the truth as this is often enough to cause someone to feel stress thereby creating nervous behaviour instead of uncovering it.
We have seen how open and closed body language can signal a desire to allow access to the body. Ventral displays show that a person is open and trusting. This is difficult to fake when people are trying to hide emotions. Another cue to watch out for is proximity displays, as it is a hint to overall comfort. People will move their torsos closer, or lean inward, rather than away, when they feel at ease and are in agreement with others. The removal of objects that impede their view, taking a jacket off, and so forth can also increase intimacy and display honesty.
Comfortable people will hold their bodies loose rather than rigid, and their body will move with fluidity. They will gesture with their speech instead of freezing instantly or awkwardly, called “flash frozen.” Sometimes people will slow down their speech to catch their thoughts and create stories. However, a good body language reader will note when the context warrants slower speech patterns such as when producing accurate answers, and when it is done in order to prevent truth telling. Comfortable people also mirror others around them instead of avoiding synchrony. Their breath rate will be similar and they will adopt like postures instead of showing differences.
Bodies show discomfort by increased heart rate, breath rate, sweating, a change in normal colour in the face or neck, trembling or shaking in the hands and lips, or elsewhere, compressing the lips, fidgeting, drumming the fingers and other repetitive behaviours. Voices often crack when under stress, mouths might dry up producing noticeable swallowing, “hard swallows”, or frequent throat clearing. Liars might use objects as barriers. They might hold drinking glasses to hide parts of their face or use walls and chairs while standing to lean against to gain support (a crutch for their lies). Liars might engage in eye blocking behaviours by covering their eyes with their hands, or seem to talk through them, or even squint so as to impede what is being said from entering their minds. The eyes might also begin to flutter or increase in overall blink rate showing an internal struggle.
Lack of touching, or touch reduction also signals discomfort and a divergence of ideas. When people’s ideas differ they find it hard to come close to others as part of the natural fear response. Head movements that are inconsistent with speech such also betray liars. A sight head nod during a denial or completing a negative thought shows a lack of synchrony which giving us evidence requiring further investigation. Additionally, when gestures are done out of sync with what is being said, they tell us that a person is adding the gesture as support for their statement after the fact. Honest people will use gestures in sync with what is being said.