Anacondas, like all snakes, shed their skin. We humans replace our skin, too, but our skin cells slough off a little at a time. Snakes shed their skin all in one piece, sliding out of it like one long sock.
Ashley laying on top of Kathleen, both are about to shed.
When anacondas are babies they shed more often (up to twice a month). As they get older and their growing slows down, they shed less frequently, unless they are in a rapid shed cycle where they shed immediately after finishing a shed. Rapid shed cycles can occur if the snake has damaged scales or other physical issues like pregnancy or a shed that didn't come off quite right. Ashley and Kathleen usually shed between 5 and 8 times per year.
A shed anaconda skin.