I first saw this a looooooooong time ago. The other day I brought it up and showed my friends. They were 100% convinced that it switched by its self, like it was rigged!! Even though some would see it go right and others left at the very same moment. So annoying, they were so stubborn.

I can get it to switch back and forth constantly, looking at the shadow of the foot does it for me...

Here's another test to see what side you use, maybe slightly more accurate although some questions have the "depends" factor.

I'm a right sided brain according to this...