I used to do this all the time when I was a kid, but forgot about it until a couple of weeks ago when drawing with Jack and Tess. It’s a great trick, and you can do all kinds of animations. We did a chicken first. If you want to try something like this, here are a couple of tips.
Draw your design on the bottom first, so you can trace over it while making the top drawing.
Leave at least an inch of blank paper at the bottom of your drawing, that way the curled paper won’t slide off of your pencil as you’re moving it up and down.