If you look through this site enough eventually you'll come across a couple different concepts some people have proposed or used, you could also do a search on YouTube and see some of the animatronics others have used, I think it's all personal preference.
The little bit of digging on this subject I've done has led me down a road letting me know I don't have the patience or talent to build something to get the moving mandibles, but I'd love to incorporate that when/if I can.