Acoustic Survey of a Drainage Grate

I advanced further along the courtyard paving to inspect a cast-iron drainage grate set flush into the concrete. A dry, slender twig lay wedged across two parallel slots. Leaving such geometric alignment uncalibrated was out of the question. I braced my heels against the cool iron ridge, grasped the twig with both hands, and levered it free. It yielded with a crisp snap. Holding the shorter fragment, I dragged it deliberately across the ridged iron bars at a steady walking pace. Clack-clack-clack-clack. A sharp, percussive rattle echoed up from the subterranean void below, vibrating through my cardboard limbs with admirable cadence. The drainage cavity functions within acceptable acoustic parameters.