Imagine looking at a light that flickers on and off. As the flickering gets faster, there will come a point when the flashes merge into a steady glow. This is called the critical flicker-fusion frequency, or CFF. It’s a measure of how quickly a brain can process visual information. Think of it as the frame rate of the movie playing inside an animal’s head—the point at which static images blend into the illusion of continuous motion. For humans, in good light, the CFF is around 60 frames per second (or hertz, Hz). For most flies, it’s up to 350. For killer flies, it’s probably higher still. To
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