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Stare at this purple square, then a white wall

A yellow square jumps out

Why do you see the opposite color after staring at one?

Your eye runs three crews of sensors

Staring at one color drains just one of them

Against the white, the tired crew answers weakly

So your brain reads the opposite color

Purple calls up yellow, red calls up green

And here's the twist: the ghost follows your gaze

Not light that lingers. Sensors that catch their breath