A basic understanding of skin structure in the area of a cutting is essential for a scene to be safe and aesthetic. Otherwise the bottom may end up looking like the main attraction in a third-rate sushi bar. A well-done cutting can be uniquely satisfying for aficionados of this type of play.
Human skin has two main layers, the dermis and the epidermis.
The epidermis has five layers which get pushed out from the stratum basale, where new epidermal cells come are formed, to the stratum corneum, which contains keratin and which dries up and falls off. There is no blood supply in the epidermis. These layers are not laid flat one on top of another like sheets of paper. Instead, the dermis has lots of folds, ridges and valleys. The epidermis lies on top of these folds and follows them.