Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a horror movie from Hammer Studios of London which also made The Reptile in 1966 and The Two Faces of Dr. Jekyl in 1960, both included on the snakes in movies list. This one is about Megaera, one of three hideous snake-haired Gorgon sisters from Greek mythology, who also include Medusa, the most well-known of the Gorgons. (Actually, they used the wrong name: Megaera was one of the Furies, not the Gorgons.) In 1900, ten years before this takes place, Megaera found her way to the German village of Vandorf where she inhabits a human form during every full moon and kills people. Anybody who looks directly at her face becomes Gorgonized - turned to stone, but if you look at her reflection, you just get sick for a few days. The usual bunch of Hammer actors in wool suits and facial hair wigs are found in this, some trying to figure out why people are dying and turning to stone, and others trying to cover it up. After she dies, Megaera loses her power and her snakes slowly retreat back into her severed head.
Fortunately, Megaera is barely seen until the very end. The movie would have been much better if they had never shown the cheesy make-up and rubber snake puppets in her hair and left her hideous appearance to our imagination. Christopher Lee admitted that the Gorgon makeup ruined the movie.