Perspective
Circle / Square
M / T
Four / Tree
Rabbit/Duck
Yes / No
| One of Raetz's sculptures in Geneva, seen as “oui” (“yes”) from one angle… | … and “non” (“no”) from another. |
 |  |
Sculpture by wiki/Markus_Raetz, photos by by Fjmustak at de.wikipedia - Own work, Public Domain
There is also a Yes/No.
Video: search
Straight Pole + Curved Hole Illusion
Straight Pole + Curved Hole Illusion - 3D print Youtube Video
