Click the green flag and stare at the black cross in the middle. Keep staring even if the project stops and don’t move your eyes from the cross! Try not to blink as much as you can. After a while, some of the pink circles may start disappearing slowly. You might also see some neon green circles!
How this works: This kind of illusion is called an afterimage. If you stare at something for a long time, the colour receptors in your eyes tire and your brain starts to tune the colours out.
