Nerves are not exact wires like the electrical connections in a computer are. They are basically tubes with a mix of chemicals, hoping that the electricity gets through. Sometimes there is a glitch in the ratio of this chemistry. This causes a wave of electricity to rush through a part of them all at once. It is in some way like a reset is for computer, it clears the wrong information out, so your nerves there can work again correctly.
When similar thing happens in the wrong area (i.e.: inside the brain, not somewhere around the butt), person can get an epileptic seizure from it.
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