Because mostly grey lines appear in the periphery, the black dots don’t appear. The image is a variation on the Hermann grid illusion, a diagram of black squares separated by white lines.

To be clear, there really are 12 black dots in the image. But (most) people can’t see all 12 dots at the same time, which is driving people nuts. “They think, ‘It’s an existential crisis ...

A dotted black line followed a character's (usually Billy's or Jeffy's) carefree peregrinations through the privet-lined, strangely carless, possibly post-Raptured streets of his neighborhood.

Learning how to draw dotted lines in GIMP can add interest to your work. How to draw a Dotted Line in GIMP. All artwork is made up of lines, and lines are the basic building block of artwork.