Shedding

Snakes shed when their skin is too small for them, and then it serve for removing parasites like mites and ticks.
when the snake shed the color of the skin changes. Moulting takes a long time in a snake life so before a moult the snake stops eating and goes to a safer place. And just before shedding the skin becomes dry. The old skin breaks near the mouth and the snake comes out helped by rubbing itself against a rought surface.

Cédric Michel
4°2