Groove on Cast Iron

I hopped right onto the center of a heavy cast-iron manhole cover set into the asphalt! The chilled surface was covered in a sharp maze of raised geometric tread patterns. Crouching low, I flicked the metallic clip on my sleeve strap along the textured iron ridge—*zrrr-clack!* The mechanical rattle echoed just like a crisp high-hat roll on a drum machine. I found a tiny, rounded white pebble on the pavement and guided it down one of the curved outer channels. It rolled smoothly with a muted metallic hum, settling right into a carved notch like a dialed-in fader switch.