Why do I have to use "global" so much when using Turtle?

[John Ladasky]

All right, never mind!

I hacked around this morning, making some changes to parts of my program that I thought were unrelated to my namespace issues.  I was paring it down to a minimal example, to post here as Ned requested.  As an experiment, I also commented out the global declaration line in move_balls... and everything worked this time.

I'm baffled as to what necessitated the global declaration in the first place.  But since the goal was to teach my students a graphical tool, I don't think that I will investigate this matter any further.