Blender 2.5 Character Animation Cookbook

Adding expressions using Shape Keys

Shape Keys, as you may already know, are saved states of your mesh that can be blended from one to another. For creating facial expressions, which can drastically change the shape of your character's face (like from a smile to an angry face), these are indispensable in the rigger's toolbox.

As a rule of thumb, you should use Shape Keys whenever a facial expression is too specific or complicated to achieve with regular bones. For instance, while smiling, the facial muscles create specific forms for your mouth and cheeks, creating skin folds (even your eyes and ears can move in a smile). Reproducing this kind of deformation with bones can be very hard, so you'd better model the specific shapes to accomplish this ...