How is a lie detector test given to a non-speaking person?

Generally a lie detector is not based on what a person is actually speaking through his mouth. On asking a question to a fellow who is dumb, one can make him write the answer on a piece of paper.
Basically there are different type of lie detectors which involves a pneumograph, a sphygmomanometer and the galvanic skin response.
Some records the depth and rate of respiration while others measures changes in physiological arousal. On the basis of physiological changes which appears in a humans body, the experts decide about it being true or false.
For more info you can visit the site LOL The Lie Detector – Does It Really Work?. Hope the answer ha smet your requirement.

Well change the topic from introduction to science

You can ask them to blink once for yes twice for no or something

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Originally Posted by juhi2011

well change the topic from introduction to science

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It's my first time! OK?

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Originally Posted by mfreecell

It's my first time! OK?

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You. It's perfectly OK. Was just suggesting u :)