[WarOnPrivacy]

> It took me several minutes before I could see the illusion. I just saw grey rectangles and pigeons smoothly moving to the right and had no idea what the “illusion” was supposed to be.

Same here. After a bit I could see some worm stretching if I focused on particular points in the image.

I noticed that as soon as I registered all of the movement, my eyes fixed a certain way that they do when I'm driving and navigating an overly complex traffic situation. I was super reluctant to try to focus them any other way.