Flutterfly
When a woman lets a fart fly, but instead of punching out the back, it rolls up the front past her vagina; causing her naughty bits to flutter rapidly. Typically caused by impingement due to restrictive yoga pants, or an awkward sitting position. These same harmonic forces destroyed the Tacoma Narrows Bridge in '40.
The combination of that lunch burrito and these yoga pants resulted in a violent afternoon flutterfly; it felt wonderful.