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1.
A little-known and poorly documented organ located directly between the stomach and rectum that allows partially digested food to bypass the rest of the digestive system. When activated, newly-eaten food will be forcefully expelled before food currently sitting in the GI tract.

The Bypass Valve is typically activated by spicy food, sauerkraut, or bad fast food. The result, inevitably, is explosive diarrhea that will contain either a) foam, b) undigested food bits, c) blood, or d) all of the above.
Oh man, that Taco Bell isn't sitting too well - I think it's going to activate my Bypass Valve!
by Clamskipper January 26, 2010