Before clicking on the image above, read this: You will see after clicking an animated image: a black visual field with a rotating grid of blue. There is a blinking green dot in the center of the field, about which the grid rotates. Fix your eyes on this central dot and then try to keep count of the yellow dots at various places in the frame. Astonishingly, you will see these yellow dots vanish! Sometimes only one disappears, sometimes two, sometimes all of them! This is not a problem with your monitor screen, it is a problem with your eye-brain system. This is another of the many excellent animated illusions on Prof. Michael Bach's website.