With some polish and more indication about which way the ball is going to go when you draw the line (and I'm drawing from head-to-tail or vice versa?), this would be an excellent mobile game. Once I understood it, I had a good amount of fun with it! I think it's interesting how you can draw another line at any moment, so I used that to avoid almost all the red orbs. You might want to find some way to limit when/where the player can draw to increase the difficulty. Great concept!