The exercise directions for Snowman (section 3.5.8) say:
If you are feeling adventurous, can you give the snowman a hat, or eyes?
A student tried this today and added a very cute beanie. Then she couldn't submit her work because Snowman seems to have a check for exactly three circles. If you have more, you can't submit it.
I confirmed this by trying to give my Snowman eyes, and when I went over 3 circles, I couldn't submit.
It would seem that a solution that would allow further creativity would be to check for 3 or more circles.