Any advice for recreating this moving pattern effect?

Support Materials and Textures
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http://michaelshillingburg.tumblr.com/post/158672241053/koya-and-bonto-i-dont-draw-much-so-making-a
The moving pattern inside of the balloon is really cool! Can anyone tell me how to recreate such a thing? (original post is by Michael Shillingburg and found on his tumblog.)