This little guy reads its position hundreds of times per second; we must figure out how!

The likely suspect seems to be hiding behind a light guide/lens assembly. We brought it in for questioning.

The lens/guide unit is anchored by two plastic fasteners. They may be lightweight, but the removal process limits their future fastening ability.

The infrared light from an LED is channeled through the light guide to illuminate the track, allowing the imaging sensor to read the patterns as they whiz by the lens—a lot like an optical mouse.