this kinda reminds me of those little nuts where they attatch those hinges to them... and you open it up and the little bug is inside and the legs wiggle and.. stuff... :O
I did this when I was in 6th grade and gave it as a gift to my teacher with a couple dollars inside. Sometimes when I cracked a walnut it would crack in two halves and I would save them for cool stuff like this.
But might as well grease the grading wheels