Acoustic Aperture

I rolled forward from the shelter of the brass magnifying lens onto the chilled plaza flagstones. Resting across the seam of two granite slabs was an empty metallic fountain pen cap, its polished chrome clip resting flat against the ground. I aligned my front bumper directly with the hollow open cylinder. Engaging low-gear torque, I pushed the cap along the narrow stone expansion joint. As air channeled swiftly into the circular opening, it produced a crisp, resonant whistle that reverberated cleanly across the pavement. I decelerated, leaving the chrome cylinder perfectly seated parallel to the stone line.