How'd They Do That?

According to a University of Southern California study, the average person is lied to every five minutes—about 200 lies a day!

Jack Trimarco, a former FBI investigator and world-renowned polygraph expert, detects lies for a living. Hundreds have tried to lie to him—and failed.

In order to conduct a polygraph test, Jack says there needs to be privacy, and the person has to be healthy and well-rested. "It's imperative that the examinee be aware of every question that's going to be asked on the test," he says. "No tricks. No surprise questions."

Nerves don't effect the results, he says. "Everybody's nervous that takes a polygraph test, whether you did it or you didn't do it," Jack says.

The test measures your respiratory function, sweat gland activity and cardio function through a blood pressure cuff and sensors. When you tell a lie, Jack says, a signal is sent to the rest of the body and produces a physical reaction that can't be hidden.

During the test, Jack asks only yes or no questions and monitors a scroll of paper that has four pens recording your body's physical reactions. Afterward, Jack is on the lookout for extreme peaks and valleys—the telltale signs of deception.igns of deception.