This piece illustrates a Hilbert curve, taken to the sixth approximation. The continuously changing color of the thread makes it easy for your eye not to lose its place as you follow the long path that starts at the top-left and ends at the top-right. http://momath.org/home/math-monday-08-30-10/
We all know stitching can be theurapeutic, but also educational. I never even heard of the Hilbert Curve, and to further confound me I don't see a curve in this piece either. But sure to be a math project no student would forget soon. I'm so glad this is shown using a variegated thread, otherwise can you imagine the boredom? Also might be fun to just do it using up small bits and pieces from your stash. It is lovely how it can make your eye dance around the surface.