Shake your head to see this image
Tuesday January 1, 2019. 09:26 PM , from BoingBoing
And if shaking your head really fast is, er, problematic, you can also just look at an angle or move away from the screen until the image appears.
Here's an Instructable on how to make your own head-shaking illusions.
Jan, Sat 19 - 08:17 CET