http://cvcl.mit.edu/gallery.htm
This is really interesting. It's all about how depth perception works. Or maybe it's not about that at all. I just thought it was cool.
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).