The Right Brain vs Left Brain test ... do you see the dancer turning clockwise or anti-clockwise?
If clockwise, then you use more of the right side of the brain and vice versa.
Most of us would see the dancer turning anti-clockwise though you can try to focus and change the direction; see if you can do it.
More discussion about this, and a justification of the hemispheric indicators at Fourouboros:
Well, maybe it depends on, ahem, what part of her anatomy we use for our initial, orienting observation. If we fix on the arc of her leg, we're not abso-positively sure of our conclusion, so we check against another part of her figure, say, her head--a universal constant supposedly. At that point of indecision, frame 19, her head appears at first glance (hah!) to be facing left. And the image proceeds to reveal nose, lips, etc. When I begin that way, counter-clockwise is easier to "see." But if you look at her head initially, which a large majority of us are wired to seek out, at least as a first step, the chances are very high that you'll perceive clockwise orientation until the brain is asked to categorize the image alongside other, more left-brain, additive, packeted info.
To me the most interesting thing is how heated some of the arguments get.
More on left/right hemispheres at Cognitive Daily.
And a curtsey to Dana Runs, a blog that I'm adding to my blogroll immediately.