If you don't see the circles, this shows what to look for:
https://i0.wp.com/mentalbomb.com/wp-content/uploads/2023/03/...
At first I saw rectangles then I searched for the circles and found them. Now I'm having a hard time going back to seeing rectangles.
________
/ \
| |
\________/
They discuss people from the educated, democratized world see rectangles while a group from Namibia see circles because, they hypothesize, their world isn't highly "carpenterized" with right angles and straight lines. So could this not be simply because they don't know what a rectangle is, and so categorize these close loops as circles? I don't understand the acceptance it is an optical illusion.