Optical illusion: Seeing color in a black-and-white image
Stare into the black circle in this video to get a lesson in chromatic adaptation from scientist Andrew Steele.
This is definitely my favourite optical illusion—it's mind-bendingly effective but infuriatingly ephemeral, vanishing as soon as you try to look straight at it—and a fantastic illustration of how our eyes and brain together conspire so that what we see and reality aren't as synonymous as we like to think.
screengrab via Andrew Steele/YouTube