Which way is the babe spinning? Supposedly, if she is turning right then your right brain hemisphere is dominant; if she is turning left, your left hemisphere is working. Very few people can see her turn both ways!
…pretty mesmerizing once you actually witness the change of spin right in front of your eyes because initially it sounds impossible to even conceive of her spinning in the opposite direction. What an amazing subtle optical illusion!
If you just don’t get it, keep staring at the page, perhaps look away for a second and focus on it again. Do not leave this page until you notice it: this is one of the best mind tricks I have ever seen!