Wow... And if you really want to see something crazy, scroll it up and down...

If you get out an image editor and compare where the pixels fade to the background grey, they are nearly, but not pixel perfect to the same height on the peaks of each row. Different peaks come to different heights. The darker shaded top left ones come up 2 pixels higher than the light ones.
Saying they're perfectly horizontal is slightly misleading. A sawtooth wave on a oscilloscope is perfectly horizontal also. Technically correct, but also omitting some key detail.

So if they don't move for me does that mean I'm dead inside?

Whoa that's making ne nauseous 😳

I can make them dance to music!

Interesting, after seeing the comments about how it works for people I can make it hold still or move. It’s wild!

I L L U S I O N S

I look at any one top or bottom edge and see it’s level.. but every thing less is slanted.
Arrrgh and they bobble..

The illusion when moving it up and down does not even break when the picture is very out of focus and viewed with one eye. So there must be something fundamental about the rough shapes and/or color grading. All the fine details are irrelevant.

Does it mean anything if they aren't moving for me, unless I scroll the image up and down? I've been told that I have field independent vision: I see parts before the whole.