Experiment with a Sunbeam

There is a sun spot on the floor in the doorway, farthest facet of a sunbeam that penetrates through the window of an adjacent room. Slowly closing the door to my bedroom, I watch to see what will happen when it reaches the spot. I expect the beam will be blocked, but instead it bounces off the back of the door and remains on the floor as a reflected beam. The glint then moves ahead of the closing door, which cannot gain on it.

Like the sunbeam constant on the closing door,
Glimpsing its reflection moving on the floor
With an independent will,
Enticingly towards the threshold sill,
I am thus barred, divided by rejection,
A constant desiring its reflection,
Clothed by the self's conspiracy,
In so nude a bum in the mirror see
The object of desire.