Where there's a face, there's also teeth and a tongue. For rigging the teeth we're adding lattice deformations. This allows the animator to push a smile for example by nudging the teeth to support the smile (depending of the style of course). It gives the animator the freedom to push a facial pose further by manipulating the lattice with control bones. The tongue is a relatively simple set up where stretch bones are used to deform the mesh, getting some squash and stretch for free. The tongue doesn't need to be overly engineert for the requirements of its movements. A simple FK setup as a base, with the additional squash and stretch usually suffices and keeps the rig light weight and easy to manage.