This is a follow up from my most viewed pen of a twitter follow button. http://codepen.io/mikemjharris/pen/yyEwVR
Two examples in this pen - one with continuous animation (mainly so that people who don't want to open the pen can see what's happening!)
The second is deployed on my blog (http://blog.mikemjharris.com/posts/svg-toggle-hack) and the animation is triggered on a hover.
More than happy to answer questions about the techniques used in this pen.