Basically you have to stare at the glamour model's negative image for a few seconds before it flips to a positive image of her tanned torso in a green figure-hugging bikini.
All okay so far. Except a few seconds later you realise the second image is actually in black and white and your brain and eyes have added the colours!
Try it – it really works!
(We went back and checked it frame by frame just to be sure!)
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