Usually best watched on Turbo Mode. Pick a size between 2 and 10 (to make sure it fits on the stage), and an 'increment' of between 100 and 200 to adjust the generated shape. The increment is actually between 1.00 and 2.00 degrees, and is the amount the angle changes by each time the pen moves.
This is a reconstruction of Euler spiral program, credit to Numberphile - https://www.youtube.com/watch?v=kMBj2fp52tA. Challenge is to explain why certain patterns are stable or chaotic, and certain patterns are similar for different increments. I think it's basic maths.
