Most of us think we know the telltale signs of a liar—shifty eyes, sweating, a long, winding story that seems highly improbable. The stereotypes are even cross-cultural: a 2006 study done at the Texas Christian University found that similar perceptions of liars exist in over sixty countries.
In reality, however, there is not one behavior all liars exhibit and some behaviors we associate with lying could mean something else entirely. Because of this, few people are very good at spotting liars. Even the so-called "experts"—body language professionals, customs officials, etc.—are only right about half the time.
Deciphering a liar from a truth-teller is not completely hopeless; it just isn't as easy as is seems. How to know when a liar tells the truth?
Can't Smile While You're Lying
After taking an online test to see if I could discern a fake smile from a real one, I realized that, like most people, I'm not very good at it. I got about 50 percent correct—not much better than chance alone. Although it can be hard for the untrained eye to detect a genuine smile from a false one, they are different, and some small clues can help you pick out which is which.
Much of this has to do with paying attention to subconscious control of facial muscles. Paul Ekman, a professor of psychology at UCSF and author of Telling Lies, developed a way to distinguish real emotions from fake ones by identifying the role of specific muscles in our face. The Facial Action Coding System (FACS) looks for things called "microexpressions," which are brief displays of real internal feelings.
Part of what he found is that although fake smiles and genuine ones use some of the same muscles, real smiles use muscles generated by the unconscious brain, meaning there are certain facial actions we can't fake.