Creating "random-ness" is...difficult

Excited to have started another online class yesterday - Carla Sonheim's Blobimal Artist Books ( http://www.carlasonheim.com/2013-summer-camp/ ). I always enjoy the drawing part of her classes. This is from Day 1:

"Jig-saw-puzzle" drawing

I found the hard part of the assignment was drawing the random blue lines (!) - somehow my first attempts just didn't look random. Huh...