Make Your Own Lie Detector

Here's something you'd never learn from Mr. Wizard: you can make your own lie detector with just two cups containing exactly the same amounts of dry rice.

The first lie detectors were being used by the Chinese 1,000 years before Christ. They used rice in a simple two-stage process:

• Fill the suspect's mouth with rice
• Ask some obvious questions to elicit a known truthful answer
• Have the suspect spit the rice into a cup and count the grains
• Fill the suspect's mouth with rice - again
• Begin the interrogation
• Have the suspect spit the rice out into a cup and re-count the grains

If your suspect spit more rice out the second time, you found your man. Think about it. The Chinese made the simple observation that when you lie, your mouth gets dry. Therefore, if you were lying, less rice would stick to the inside of your mouth and you would spit more back into the cup. The question with the known truthful answer was a control to see how much rice would stay in your mouth when you weren't fibbing.

The Chinese lie detector worked on the same principle as modern devices: telling lies results in a predictable physiological response. If you can recognize and interpret that response, you can asses whether or not a person is lying.

Why do lie detectors work? As I understand it, they work because lying is an unnatural act, and the human body rebels against this act in measurable and predicable ways.