<unk> , also known as piss shivers, pee shivers, peegasm or whiz willies, is a phenomenon in which one feels a shiver running down the spine following urination.  
The shiver can produce a brief twitch, which is a form of myoclonus.
To date, despite years of Internet discussion and theorizing, there is no agreed-on explanation of the phenomenon and no medical research into it. However, it has been mentioned occasionally in columns, and in one internet poll, where about 83% of males and 58% of females reported experiencing it.
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