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 fun, campy horror movie starring Vincent Price as Dr. Anton Phibes, a scientist and organ-playing biblical scholar who wears a hooded cape and a wig and prosthetic makeup to disguise his head that resembles a human skull after its hair and skin was burned off in a car crash. He needs to plug something into his neck that is connected to a speaker just to talk, and he also eats and drinks through the hole in his neck, but he still seems to have superhuman strength. He has a band of life-sized mechanical musicians in his lair that he winds up to play a tune so he can dance with his beautiful mute assistant and chauffeur, Vulnavia (Virginia North) who looks like a high-fashion model and wears a succession of elaborate outfits and silly hats.
Phibes is seeking revenge on the nine doctors who he believes were responsible for his sick wife dying on an operating table. He kills the doctors one by one, using his version of the ten plagues visited on Egypt to persuade the Pharaoh to release Moses and his people, or the G'tach - boils, bats, frogs, blood, rats, hail, beasts, locusts, death of the first born, and finally darkness. We learn from the bumbling detectives at Scotland Yard that one doctor was killed by a swarm of bees. We see another doctor killed by bats, and another killed at a costume party when Phibes fits him with a large green frog mask that slowly tightens until it crushes his head. One doctor is chewed up by rats as he is flying an airplane which makes him crash. Another doctor is killed by the horn of a giant unicorn statue that was catapulted through a window at him. Another doctor is frozen to death inside his car. Phibes pours green goo made from Brussels sprouts through a hole in the ceiling onto a sleeping doctor's face then releases locusts into her room to eat the flesh off her bones. Phibes keeps a wax statue of each doctor that he melts with a blowtorch after he kills them.
The snake appears when we see one of the doctors, Dr. Longstreet (Terry Thomas) in his home. His housekeeper Mrs. Frawley tells him that she is going out for the night. He is obviously excited about being alone so he can watch a dirty movie. The year is 1925, when there was no internet porn, so he has to watch a silent movie of a scantily-clad woman dancing with a snake. It's so tame by today's standards, it wouldn't even be banned in Florida.
We see Dr. Longstreet having a drink while projecting the movie on a small screen. The woman takes a large Boa Constrictor out of a basket then holds it up and dances around with it, finally putting its head in her mouth. From his facial expressions we can see that he is getting very excited, at least until he sees Mrs. Frawley standing behind the screen, which is stretched across a doorway. Later, Phibes and Vulnavia sneak into his home where she entices the doctor then ties him to a chair. They drain the doctor's blood into jars, leaving him completely drained and dead. That's the "blood" part of the ten plagues.
The movie was followed by a sequel, Dr. Phibes Rises Again, which also has a great snake scene.
You can watch the snake scene, which starts at about 18 minutes and 50 seconds, or the whole move over at TheSilverScream.com.