Subsurface scattering

Why you can see trough some objects

Subsurface scattering (SSS) is a mechanism of light transport in which light penetrates the surface of a glowing object is scattered by interacting with the material. The light usually penetrates the surface and reflects a number of times at irregular angles inside the material before passing back out of the material at an angle other than the angle it would have if it had been reflected directly off the surface.

Why does artist have to about SSS?

In order to create realistic 3D computer graphics, it is necessary for artist to understand this mechanism and create/render materials such as marble, skin or leaves with SSS and achieve realistic objects and or graphics. One method to create SSS is by estimating the distance from the light source to your object.