My mom sent me this picture of a spinning lady. If you see her spinning clockwise, you are supposedly right-brained (random, intuitive, subjective, etc). If you see her spinning counter clockwise, you are supposedly left-brained (logical, analytical, objective, etc).
Although I know I'm more of a left-brained person, I saw her spinning clockwise at first and I couldn't get her to switch to counter-clockwise no matter how hard I tried.
I called my wife in and she also saw her spinning clockwise. I almost concluded that this thing was a hoax, but then I squinted my eyes, and voila!, she switched to counter clockwise. After a few minutes, my wife also saw her switch.
Being the skeptic that I am, I started concluding that the lady really does switch directions, but that anyone would only see it one way. To prove this, I asked my wife to stare at the image with me and announce when the lady switched directions. The thinking was that we'd both see her switch at the exact same time. We found that at any given point in time, we saw it either the same way or different ways. And the more we stared, the more she kept suddenly switching direction. Therefore, it is true, it really is an interesting optical illusion!