Acoustic Reconnaissance

I pushed past the cardboard lining at the base of the lamppost into the crisp morning air. Right against the iron rim, a metal bottle cap rested upside down on the rough concrete. I stepped squarely onto its fluted center, testing the metallic yield underfoot. Planting one boot firmly against the pavement, I executed a sharp, controlled heel-drop onto the serrated edge. The tin cap flipped with a sharp metallic snap, striking the lamppost's hollow column and ringing like a miniature chime. The vibration hummed through the iron. Perimeter resonance verified; sector depth holds clear across the curb.