I have tabs, so I had to pull the tab out to a new window (or else risk resizing everything that is already the way I want it).
I don't know how wide my windows are! I had to pull up the javascript console and read "window.innerWidth" and 320 is amazingly small for me.
Reason for the resizing down at the start is simply so only certain parts of the animation show at different times. It means I can control what width the animation is being viewed at, as otherwise I'd have to animate everything across a very large width potentially, which would be pretty time consuming, as this could be huge. Think with the feedback I've had, will release as a non media query animation as well when I get chance.
There's nothing ground-breaking here, but neither is there in many of the XKCD stunts that we fawn over here. I think if you just describe it that way we'd all know what's going on.