<P> Butterflies in the stomach is the physical sensation in humans of a "fluttery" feeling in the stomach, caused by a reduction of blood flow to the organ . This is as a result of the release of adrenaline in the fight - or - flight response, which causes increased heart rate and blood pressure, consequently sending more blood to the muscles . </P> <P> It can be a symptom of social anxiety disorder . The symptom of this phenomenon is usually experienced prior to attempting to partake in something critical . </P>

Where did the idiom butterflies in your stomach come from