Ha! It took me awhile to figure out that I was supposed to click the ball. At first I was thinking "Hey this is kinda cool, I like physics. It's like my classical mechanics class, only with non-physics string." and then "Ohhhhh you want me to click it..." and proceeded to give myself carpal tunnel because I'm on my laptop with a touchpad.
This would be no problem with my nice gaming mouse, but on my laptop, no way.