The term "snake possession" means something very similar to "ghost possession" in tales of the supernatural.
It means another autonomous soul has entered your body and taken it over.
Cases of animal possession have long been documented in nature, with the most well-known example being the Weasel.
Folklore has long warned that no matter what animal you offend, you must never cross a Weasel. These creatures are highly spiritual, hailed as Earth Immortals.
It is vengeful to a fault. If you offend it, it will possess you and make you do all sorts of bizarre things, plunging you into a state worse than death.
The Weasel, or Yellow Immortal, and the Snake, or Snake Willow Immortal, are part of the Five Great Immortals of folklore—all of them highly spiritual beings.
This is especially true for the awakened ones; they are not to be crossed lightly. Even an accidental offense will bring disaster raining down from the heavens.
