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A person is not static charged. But if the air is dry, the person is insulated from ground and combs his very dry hair or removes a very dry sweater then he can become static charged until he touches something that is grounded.
I had some shoes with synthetic (plastic) soles. At work the carpet was synthetic (plastic). My shoes and the carpet were very good insulators and in winter the air was very dry. When I shuffled my shoes on the carpet as I walked I developed a very high static voltage and I zapped anybody who came near me. A long spark jumped from my finger and the telephone system would reset. I got leather soled shoes and the static stopped.
We talk about electronic circuits here, not physics.
The lie detector circuit is a simple ohm-meter. Some people (not everybody) sweat when they say a lie. The sweat reduces their skin's resistance and the ohm-meter shows it.
Then add 2 more pages of blah, blah, blah etc.
Look at Lie Detector in Google. There are many other things to sense plus a lot of experience reading them to guess that a person is saying a lie.
This is based on the fact that when people lie they presumably sweat a bit because they are stressed. So many co-factors could explain the jumping of the multimeter, e.g. the lights in the room are too hot making the hand sweet or that theyr scared your going to shock them with your scary looking lie detector