This image has been a source of amusement in my office for the last couple of days. If you look at the image, you can sometimes see the dancer change the direction of her rotation.  But it's not an indicator of Right/Left Brain dominance as some people have said (read the article below).

Everyone in my office could see it change except for my sister.  She probably would have thought it was a prank if it weren't my mom exclaiming every time it changed direction for her.  My sister was convinced that it only rotated clockwise until she saw it change about 10 minutes later.

From NYTimes.com: The Truth About the Spinning Dancer

But while the dancer does indeed reflect the brain savvy of its creator, Japanese Web designer Nobuyuki Kayahara, it is not a brain test. Instead, it is simply an optical illusion called a reversible, or ambiguous, image. Images like this one have been long studied by scientists to learn more about how vision works.

Sometimes, a person will stare at an image and it will never reverse. Dr. Toppino advises staring at one part of the image, such as the foot, and most of the time it will eventually flip. I tried this several times, but it never flipped. Dr. Toppino says in people who can't see the reversal, it may be that one underlying neural structure is more dominant, but once someone finally manages to see the flip, it will start to happen more often.