[carlosjobim]

Fun fact: Some of the sandwiches seem to be rotating in the opposite direction. This is due to an optical illusion called the "Silhouette Illusion" [0], first discovered in 2003. If you focus hard on a sandwich and blur your eyes slightly, you can make it change which direction it rotates.

[0] https://en.wikipedia.org/wiki/Spinning_dancer

[doctoboggan]

I am assuming you are joking but I see other people responding as if you aren't.

This isn't true as the spinning dancer illusion only works on silhouettes and not full color images.

[oceanplexian]

I squinted at the sandwiches trying to reverse their direction like an idiot. Guessing I’m not the only one.

[JKCalhoun]

The dancer illusion is as though you are observing the dancer from a long distance away through a telescope of some sort where things like her hands do not appear to vary in relative size as she turns and they become nearer/farther from us.

[StrictDabbler]

It also works on translucent objects and in a different form on the mask illusion, where a rotation depends on whether you believe the mask is bent away from or toward you.

Basically anytime that depth information is obscured.

[jon889]

I can't see how this is correct. The spinning dancer works because there's no details on it.

[evan_]

I was skeptical as well but after looking into it further I can confirm that it's actually true. The brain is amazing!

[ydant]

I still don't buy it - looking at these two in isolation:

https://rotatingsandwiches.files.wordpress.com/2023/02/banh-...

https://rotatingsandwiches.files.wordpress.com/2023/02/shrim...

Very "clearly" spinning in opposite directions.

[wunderlust]

The ambiguous effect of the silhouette dancer is real, but some of the sandwiches really are rotating in a different direction from the others.