The turning dancer.

Have you guys seen that dancer that turns in different directions? The turning dancer

I thought I finally understood it... but I think I may have been wrong.

Okay... I did an experiment where I just let the image run for a while. After about two minutes, I discovered that the image appeared to speed up and then switch directions from clockwise to anti-clockwise... I refreshed the page, and the image returned to going clockwise.

So I performed the experiment a second time, and again, after two minutes, the character began moving anti-clockwise. "Aha!" I thought! This cannot be real, then! So I refreshed the page again.... Still anti-clockwise. I refreshed again. Still anti-clockwise.

Strange. So I downloaded the GIF and loaded it into my image editor. Only 34 frames at 30ms each, totaling about 1 s of animation. There's no way that *this* GIF could possible be switching at 2 minutes... I'm wondering now if there's some sort of Javascript thing going on...

While doing this, I kept glancing back at the damn picture. Still anti-clockwise.

Once I finished, I looked again. clockwise.

This makes no sense.

I refuse to rest until I understand what's going on and how to make it switch back and forth at will, or figure out the underlying trick.

*blinks*

Wait a sec... If I stare at the text and let the image reform a little... I think I can manage to get it to shift to counter clockwise. But as soon as I look at her foot, it goes clockwise again.

*nods* Got it... I can do it at will now.

Fascinating... It seems difficult to hold it in "anti-clockwise" rotation.

aha! The illusion explained!