Teeth and Links

I traversed the flagstones toward the rear wheel of a bicycle leaning against the courtyard fence. Its lower derailleur hung suspended just inches above the gravel. I paused to inspect the linked drive chain threaded through two small guide cogs. Bracing my foot against a brick edge, I reached up and pressed my palm against the tension arm. The internal spring yielded with firm, deliberate resistance. When I nudged the lower jockey wheel forward, the teeth meshed into the chain rollers with three muted, metallic clicks. The interlocking geometry functioned with complete precision.