This post from Chris Voss, a former FBI hostage negotiator and author of "Never Split the Difference," originally appeared on Quora as an answer to the question, "What are some good signs to watch for when reading nonverbal signals?"
The No. 1 nonverbal signal to look for is really a change. This is actually the way a polygraph works.
People being interviewed are given the baseline questions (ones they should tell the truth about) and are then hooked up to quite a number of probes designed to detect physical changes: changes in breathing, head movement, eye and head movement, hand gestures, etc.
"What did you have for breakfast?""Where did you grow up?""What did you like about where you grew up?"
If, while they are answering, a change is caused anywhere, then the person is likely practicing some form of deception. This could correlate to a weakness in position they are trying to cover up.
Additionally, hands covering the mouth as a response to questions are often a sign of discomfort with the answer — possible deception.
The flip side might be asking them something you know they'll be caught off guard by, and know they aren't completely sure of the answer: "Have you got complete authority to make a deal?" Since no one has COMPLETE authority, their response likely just gave you their first (and go-to) "tell"— the physical move that is "telling" about a lie or some sort of deception.
There are a number of common moves for lying, but not common enough to be sure with each person. There a great Jimmy Kimmel episode I show a lot of my clients and students called "Lie Witness News." If you watch it, you see the 4–5 common ways people lie. Each person might manifest a different way depending on the circumstances.
Despite the variety of ways people might lie, everyone pretty much has only one way they as an individual tells the truth, if they tell the truth. Get a bead on that and then look for physical changes to indicate deception. If you ask them a question that you know the answer isn't true and you see no change, that means they're deceiving all the time. Good information to know as well.
SEE ALSO: How to be an excellent negotiator — even if you're shy
Join the conversation about this story »
NOW WATCH: Former Navy SEAL Jesse Ventura says 'American Sniper' Chris Kyle shouldn't be remembered as a hero