AMBIGUOUS ILLUSIONS
The owl-moose, along with other famous illusions like the Necker cube and the young woman/old woman image called the Boring figure (named after the psychologist who wrote a famous paper about it, not how exciting it is) are known as "ambiguous figures." And what makes them special, of course, is that sometimes they look one way, and sometimes another; in this case you either see a moose or an owl. They are among the studied types of images in neuroscience, helping scientists understand how the brain, so to speak, makes up its mind.
