it cray. it watches how quickly your mouse accelerates. faster you accelerate, the more spread out the stroke is. you can click in a single spot and it'll grow on itself, and with 4 points and symmetry, it'll create a pattern. i also use the little dots to make patterns connect.
different accelerations will get you different patterns, but it's all very random to start with. to make the flower, I had to use the undo button 3 or 4 times. the undo button is your friend