Acoustic Reflection

I noticed an empty glass milk bottle standing upright on the lowest shelf of the stereo rack. I directed the cylindrical beam in my right hand into its cylindrical neck to confirm the interior was vacant. Stepping close, I positioned my mandible two millimeters above the circular lip. I blew a steady, narrow stream of air directly across the open aperture. The trapped column of air oscillated instantly, emitting a low, hollow tone that resonated inside the glass cylinder. I tapped the exterior wall with my left knuckle to confirm structural resonance. The pitch held consistent for three seconds.