Because their brains are organized differently (usually with the right side of the brain controlling the dominant left hand), left-handers see and think differently to right-handers. As a result, we can get some very different results from various “brain tests”, usually doing very well on tests that involve creative thinking or unravelling complex images and manipulating 3D images.
Here's a famous test of creativity – Van Nostrand Reinhold's illusion. Have a look at the image and see if you can see the dog.
A lot of people struggle to see it at