In addition to other questions, both sites ask students to determine how the image was created–a nice enough problem for students learning to play with areas of circles. This immediately reminded me of the construction of the yin-yang (ignoring the “eyes”, of course).
Personally, I would lead with that and then shut up to let them think. Students are remarkably insightful when we allow them to be, and too often a teacher’s desire to be “helpful” robs students of key opportunities to be creative and to grow. (I’ve certainly been guilty of this.) The reality is that I’ve often learned far more from inspirations gleaned from my students’ musings than the questions I posed for them in advance. Whatever generalization(s) they determine, my sole insistence is that students prove their claim(s).
Another nice extension of this is the arbelos. So much cool math in this shape.