....a green green green snake winding around a branch. Seen in the Aquarium of the Berlin Zoo. This is Morelia viridis, a "green tree python" found in New Guinea, Indonesia, and Cape York Peninsula in Australia.
A snake is a scaly, limbless, elongate reptile from the order Squamata. A literary word for snake is serpent (from *serp-, "to creep").
Serpent however is commonly used in a specifically mythic or religious context, signifying a snake that is to be regarded not as a mundane natural phenomenon nor as an object of scientific zoology, but as the bearer of some symbolic value.