ha! now I see it too. But it's an illusion caused by the frame rate and the animation speed. if you try to imagine the pink gear turning correctly, eventually your perception will snap and it will appear correct again.

for me I can't see it any other way. When I watch the teeth meshing, they look correct, but when I zoom out, the other side of the gear is always going backwards

It seems like one of those trick your mind animations

now that you've linked it, I feel like it's easier to ingest his information directly from YouTube. Wonder whether him as the author, would prefer that or his own website