Movie #1(Above left) : Silvanus P. Thompson, in "Light visible & invisible" (1897) noted that when a cogwheel pattern moves along a CW path, it shows an illusory counter-CW rotation. (I admit that these movies do not work all that well. Try jiggling a paper version.)

Movie #2 (Above right): Low contrast cogs seem to rotate CW. I don't know why.

Movie #3(Above left) : Hedgehogs with outward-pointing teeth seem to rotate CW.

Movie #4 (Above right): Simulation & explanation. Top left: When only the outer tips of hedgehog teeth are visible, they rotate strongly CW. Top right: When only the inner teeth of cogwhels are visible, they rotate strongly CCW.

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