Detecting high-stakes liars is often the work of the FBI, and they frequently look to facial expressions, body language, and verbal indicators as signals, or "tells," that someone is lying.
Mark Bouton, an FBI agent for 30 years and author of " How to Spot Lies Like the FBI ," tells Business Insider that he used certain tells to help identify Timothy McVeigh as a suspect in the Oklahoma City bombing. But being able to read facial expressions to detect lies can be beneficial even if you're not conducting criminal investigations, he says.
"There are a number of facial expressions and associated reactions that could indicate someone is lying to you," he says. "Some are caused by nervousness, some by chemical reactions, and others by physical reactions."
To start, he says it's important to understand how the person in question normally acts.
"It's best to observe someone for a while as you make small talk or ask innocuous questions, in order to see what his usual reactions are, including tics he may have," he says. "Then if he exhibits several lying indicators when you ask more pointed or suggestive questions, and these are not ones he previously performed, you can be confident that he's likely lying."
Here are some things you can do to tell if someone's lying:
Watch their eyes
"This is a physiological reaction to him feeling uncomfortable or trapped by your questions that he doesn't want to answer," Bouton says. "It's a throwback to when people had to seek an escape route when they feared they were in a dangerous situation, such as facing a human or animal adversary."
Keep an eye out for rapid blinking
"A person will ordinarily blink about five or six times a minute, or once every 10 or 12 seconds," Bouton says. "When stressed for instance, when someone knows he's lying he may blink five or six times in rapid succession."
Bouton says exceptions to the usual blink rate mostly have to do with production of dopamine in the body. For example, a person with Parkinson's disease will have a noticeably slower blink rate than what is usual, while a person with schizophrenia will blink more rapidly than normal.
Count how long someone closes their eyes
Bouton says that when a person closes his eyes for a second or two, this may indicate he's liedto you, since this isa type of defense mechanism. Normally, he explains, a person will blink at a speed of 100 to 400 milliseconds, or 0.10 to 0.40 of a second.
Pay attention to the direction they look
"When you ask a normal, right-handed person about something he's supposed to have seen, if he looks upward and to his left, he's truly accessing his memory of the incident," Bouton says. "However, if he looks upward and to his right, he's accessing his imagination, and he's inventing an answer."
Bouton saysthat left-handed people will usually have just the opposite reactions.
And some people will stare straight ahead when trying to recall a visual memory, he says.
Take note of what you're asking them
"If you ask about what a person heard, his eyes will shift toward his left ear to recollect the sound he heard, but if his eyes shift toward his right, he's about to fib," Bouton says.
The key is in what they're trying to recall
"His eyes will shift downward and to his left if he's going to tell you his memory of a smell or touch or sensation, such as a cold draft or a terrible odor," Bouton explains. "But his eyeswill shift down and to his right if he's going to lie."
Bunched skin beneath and wrinkles beside the eyes indicate a real smile
Bouton says that when people genuinely smile, the skin around their eyes bunch and wrinkle.
Watch their hands as well
Bouton explains that a chemical reaction causes people's faces to itch when they lie.
And keep an eye on what they do with their mouth
"A person's mouth will often go dry as she's lying," Bouton says. "She may do a sucking motion, pursing her lips, to try to overcome this."
When their lips are so tightened that they appear pinched and white, this can indicate lying.
Take note of any excessive sweating
Bouton says sweat may appear on the forehead, cheeks, or back of the neck, and you'll likely observe the person try to wipe it away.
And in some instances, notice when the person blushes
Blushing is an involuntary reflex caused by sympathetic nervous system (this activates your fight-or-flight response) and is a response to the release of adrenaline.
Pay attention to which direction they shake their head
Often when people tell the truth they will nod their heads simultaneously in agreement with what they're saying. But if they shake their heads in disagreement with what they've said, their bodies are betraying their lie.
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