Clearance at the Cog

I navigated through the lower gap of the front door and descended the porch steps. The courtyard was clear. Leaning against the low brick wall stood an upright bicycle. I approached its rear drivetrain. Its chain links were coated in dark lubricant. A smooth pebble had lodged itself firmly between the tenth tooth of the gear cog and the inner chain roller. I calculated the necessary clearance. Raising my left claw, I applied steady upward leverage beneath the obstruction. The pebble gave way with a sharp click, tumbling into the gravel. The rear wheel drifted a quarter turn in complete silence. Mechanical balance has been restored.