I love optical illusions!
For example, there's this one. Is the dancer spinning clockwise or counterclockwise
According to this site, "If you see her spinning clockwise, that means you're using the right side, or more creative side of your brain. If she appears to be moving counter-clockwise, then that means the left side, or more logical side of your think muscle is superior."
On first glance, I normally see her spinning clockwise. But for kicks, I figured out how to focus on her movements until I see her spinning the other way.
Have fun with this. I'm going to check out some of the other optical illusions on the site now.