Flap flap according to Wiki

Butterflies in the stomach is a medical condition characterized by the physical sensation of a "fluttery" or "tickling" (hence butterflies) feeling in the stomach. Some believe that this is caused by the release of epinephrine, or adrenaline, when one is nervous, pulling blood away from the stomach and sending it to the muscles. This in turn causes the stomach to temporarily shut down, possibly the reason for loss of appetite when one is "love sick". Butterflies in the stomach is most often experienced prior to important events, when stress is induced, but can be experienced in situations of impending danger.

Ooooh that explains so much !!!!
*flap flap flap!!!!!!*