I'd like you to clasp your hands together and keep them in that position for a moment. Some researchers see the brain as having two general modes. In one mode, often called right-brained, it's more intuitive, visual, and creative. In the other, often called left-brained, it's more logical, sequential, and analytical. All of us work in both modes but naturally tend towards one or the other.
According to the theory, if your right thumb is on top of your left thumb, then you tend to be a so-called left brainer, and so are more likely to be verbal and analytical. If your left thumb is on top of your right thumb, then you tend to be a so-called right brainer, and more likely to excel in visual, creative, and intuitive tasks.
So if you want to gain a fun insight into somebody, maybe you should ask them to put their hands together.