This sandmold will create a so-called Ambiguous Cylinder that SEE-mingly (pun intended ;-) ) changes its shape when viewed from the other side.

These were shown by Kokichi Sugihara in Japan.

See also my other models using he same effect:

https://www.printables.com/model/203213-ambiguous-cylinder-pen-holder-circles-and-squares

https://www.printables.com/model/368985-ambiguous-cylinder-pen-holder-triangles-and-circle

https://www.printables.com/model/368995-ambiguous-cylinder-pen-holder-hearts-and-diamonds