Animated gifs will not be animated when resized. I see that you’re using the full sized image, but there are parameters added to the src attribute (probably due to some plugin or your theme):
From the source:
<img class="size-full wp-image-4604" title="Koch snoflake progression" alt="" src="http://wewanttolearn.files.wordpress.com/2012/10/snowflake-diagrams1.gif?w=545&h=472" height="472" width="545">
Take off the parameters ?w=545&h=472
, and it should work. Leave the width and height attributes on the image, and it will still be displayed at 472×545. Tested it in Chrome dev tools, and it worked.
Fixed:
<img class="size-full wp-image-4604" title="Koch snowflake progression" alt="Koch snowflake progression" src="http://wewanttolearn.files.wordpress.com/2012/10/snowflake-diagrams1.gif" height="472" width="545">