Did you see it? After about 30 seconds the swirls of colour disappeared entirely. Posted to Reddit by NightBreeze13, it’s an example of a phenomenon known as Troxler’s fading.
Derek Arnold, a psychology professor at the University of Queensland, told The Verge that the reason the colours disappear is because the brain stops paying attention to visual scenes that don’t change.
Every year, Scientific American runs the Best Illusion of the Year Contest to celebrate illusions and perception. The winner of the 2017 competition, 'Shape from Motion Only' will leave you scratching your head: