Membrane. Each slab has a meat side and a bone side. The meat side is convex (curving towards you), and the bone side is concave (curving away from you). The bone side has a membrane called the pleura covering it. It can be leathery and almost unchewable when cooked, and it can prevent flavorings and smoke from penetrating. Many butchers remove the skin. If the membrane has not been removed when you bring home a slab, you should remove it yourself.