In this video excerpt from NOVA scienceNOW, learn about polygraph tests and lie detection. Correspondent and New York Times technology columnist David Pogue commits a staged crime and undergoes a polygraph test to find out how it works. Lying can cause stress, which produces common physiological responses, such as an increased heart rate and sweating. Polygraph testing experts explain what the test measures, why the questions are reviewed in advance, and why the test doesn't always work.

This video is available in both English and Spanish audio, along with corresponding closed captions.