A little example showing how animation-play-state can come in handy. The video tutorial version is on vimeo: http://vimeo.com/61477511
Also, you're getting a cool circular saw when you change the animation duration to 1 second :)
why isn't it working in this codepen?
Looks like I moved the image that this Pen uses since this was made years ago before CodePen could host assets. I'll see if I can find it and link it up again. The code still works, you just can't see it because it's white on white without the background image.)
Need to know how to enable it? Go here.