This article summarizes the use of edge loops in mid-res polygonal facial modeling and related anatomical theory.

Waiting for Jell-O
Faces are weird objects. Mechanically, a face is a nylon sock full of pressurized Jell-O mugging a hydraulic cash register wrapped in sentient rubber bands. It stretches and puckers, slobbers and sloshes, and rattles all around, especially in flap-n-snaps.
Modeling such a thing in 3D so that it looks natural when it’s moving is tricky. There’s a technique known as an edge loop which is useful in this situation, but to use it successfully you must understand the theory behind it.
When modeling for animation, potential motion must be taken into account. Certain shapes allow for certain motions, and other shapes will fight attempts to be animated. In general, edges or boundaries between shapes act as hinges, allowing bending, and extra detail allows expansion without distortion, like the corrugations in a bendy straw.
If available memory and processor power were infinite, an infinite amount of edges and detail would allow for any motion, limited only by the rig — however, here in reality we must find a balance between the amount of detail in the model (aka its weight) and functionality.
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