Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
A man and his wife move into his deceased brother's cottage in a small village in England where people are dying mysteriously with twin bite marks on their necks. A Doctor of Divinity who has travelled the world studying ancient cultures, once wrote about a secretive religious cult in Borneo known as the Snake Cult. As revenge for telling the world about them, the cultists put a curse on his daughter, Anna, making her change into a murderous snake monster. One of the cult members follows them to their large mansion in England to make sure her father doesn't try to kill Anna.
We don't know what makes Anna change her shape. Sometimes we see her as a normal young woman, one time she was dressed in a sari playing a sitar, and sometimes she has two fangs and a scaley head and she bites people on the neck. She doesn't eat her victims, she only bites them, which is typically stupid movie monster behavior. Real dangerous beasts don't kill for no reason.
Her father says that in the winter she sheds her skin and sleeps, and he keeps her in the basement next to some hot sulphur springs to keep her warm. At the end somebody breaks a window and she complains about the cold and immediately drops to the floor, either dead or just sleeping, we don't know.
The only real snake seen in this movie is a stuffed cobra, but it does its best to terrify an unsuspecting visitor who trips and falls in front of it in a dark room.