Sentence:  Years of practice had taught us the art and a certified <WSD>eyeballer</WSD> can be staring at his feet and shoveling all day in a perfect frenzy. But all the while he is staring into the burnished pan of his shovel, which catches the reflection of a chrome hub cap whirling by on the road. And in that infinite glimpse he catches the spinning vision of a distant window behind his back, in the frame of which there is the flash of a polished doorknob reflecting around the edge of a doorway to capture on its rounded surface the distorted image of a woman removing her housecoat and putting on a brassiere. 
Meaning of the word marked with <WSD> tags:  A voyeur or inquisitive person.