What is the expression of the man on the left ? And the woman on the right? Now, take a few steps back or squint your eyes: how do their expression change?
On a close-up view, you can see that the man on the left is frowning and on the woman is calm. right face, a woman with a placid facial emotion. But further back, the faces change expression and even genders! If you squint, blink, or defocus, the angry man turns calm (left) and the calm woman turns angry… and male (right).