The mouth becomes a potential for undercut problems, particularly if the mouth is cast partially open, which is what I recommend.
Surface anatomy of the skin varies on different parts of the body. For example, the skin covering the shoulder and arm is smooth and very movable over the underlying muscle and bone. Over the inside and front of the forearm the skin is thin and smooth and has very few hairs. The skin on the outside and back of the arm and forearm is thicker and denser and contains more hairs. Around the elbow, the skin is thick and rough and is very loosely connected to the underlying tissue so that it falls into transverse wrinkles when the forearm is extended.[12]