Sentinel - Capture In Progress
Right after you start monitoring a page, this is the loading gif that appears when we haven't finished taking the screenshots yet.
This effect is done in CSS3 entirely and is a complete and shameless ripoff of http://tobiasahlin.com/spinkit/ :-)
It is surprising how much CPU it actually takes to render this animation. I'm not sure I can reliably use it in production - we'll see with the feedback on our future users.
