This article is from the Car Audio FAQ, by Ian D. Bjorhovde (ianbjor@mobileaudio.com) with numerous contributions by others.
Nothing. This is caused by static buildup by rubbing against the seats,
floor mats, etc., just like walking across a carpet in a home. You can
avoid this shock by touching something metal on your car _before_ you
put your foot on the ground.
 
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