Thread: Cordovan vs. Shell vs. Horsehide?

Shell is actually produced from a part of the subcutaneous muscle layer in horses, and other mammals, called the panniculus carnosus. Humans have a similar thin muscle called the platysma (in our necks, not our butts).

This muscle in horses is what allows them to flinch their hide to shoo off flies.

In humans, this same muscle layer (platysma) allows us the ability to make the WTF face.