Modern browsers allow pages to modify part of the displayed URL using a mechanism called history.pushState; this is used to give you a copy/pastable URL without relying on URL fragments or reloading the page. It's currently most famously in use by the new (2010) Flickr website.
While it was intended for useful uses, instead we're going to use it for animated uses. Watch your browser's URL bar while clicking on the linkes in the following demo:
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