Sometime during the discussion, we arrived on the topic of space perception and optical illusions.  I wonder if this optical illusion works on everyone [who isn't blind], and if there are people it doesn't work for, why doesn't it work for them? Also, why does it work in the first place? Why is it that the image can't stay still when I move my eyes about it- when I move from one loop to another or if I move toward and backwards from the image?