How I broke a wine glass with my VOICE (using science!)

Whoa that was neat. This vid really got the wheels spinning.. I *think* the inward curve of the glass toward the stem is your blemish, not necessarily pre-existing cracks. The longer an audio wave travels across a rigid surface, the broader its waveform - when met with an edge, the wave is reflected. That edge termination (curve) significantly affects the shape and direction, thus resulting sound, of that wave. Sooo maybe singing at a different spot on the glass will lessen the time it takes to hit that crit point.. or even allow one to change the orientation of the crack?