They don’t. Thier muscles contract. If you brush against an electrified object while walking, you’ll go stiff and fall over as all of your muscles contract, but if the electrocution doesn’t kill you or knock you out, you’ll have bodily control again the instant you lose contact with the electrified object.
However, if you reach out and grab an electrified object, your muscles will contract and your grip will be “locked” onto the object. Or if you fall on an electric object you’ll go rigid and can’t move to get off of it.
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