It's a cool one, my brain isn't sure what way the image is spinning (or appears to be spinning I should say), clockwise or anticlockwise, so it tends to flicker between both. I can do it on and off without letting a single rotation of either slip in too, by getting blurry eyes and pining from left to right at about the same tempo as the animation, but only for a few seconds, my eyes fill up with water and I have to blink.
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