This is Google’s first doodle made entirely using HTML5 canvas, so you need to use a modern browser to interact with it. It runs a physics simulation on the mobile’s geometry, and then does realtime 3D rendering with vector graphics. Only recently have browsers advanced to the point where this is possible.
Mashable:"We noticed the interactive animation works on Google‘s Chrome 12 browser, but not on Firefox 5.0 or Internet Explorer 9. We’re also seeing reports that the animation causes a crash in Firefox on Linux, so if that’s your browser, you might want to avoid this doodle. Note that others are reporting these browsers are able to display the animation. Best way to find out if yours works is to go to Google.com and try it."