Just a little insight to the process on how Laika gets some of there mouth shapes courtesy of David Vandervoort. I really think it's a great example of nice shapes that flow organically in and out of each other. The timing of how you get from one shape to another and even how long you can hold a shape really takes some practice and refinement to get it to look organic. It reminds me of a lecture I had at work a couple of years back on Swing Sets (remember these words).
Enjoy and even try to download so u can frame through the shapes...pay attention to how the jaw moves...really nice!