Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
TheSilverScream.com describes this as an American horror film and blaxploitation movie that is a different take on an "Old Dark House" mystery as well as very much a voodoo movie. (You can watch the full movie and read a synopsis of it there.) It's about a dying old woman and voodoo practitioner named Pauline Christophe who makes a will and invites all of her heirs to come to her house on a mountain with a large rock formation that looks like a skull. By the time they all get there, she has died. Circumstances force them to stay there for a few days before the will can be read, and one by one they start dying. Snakes are used in several scenes to scare or to kill them, but they may not be real, only hallucinations caused by voodoo spells.
Phillip, the grandson, is first found dead, though no snakes were involved.
Next we see the granddaughter Harriet enter a room where she is startled when she sees a rattlesnake on a plant arrangement inside a glass container. But she leaves unharmed.
Then we see Harriet in the house when the locked door to her Granmother's room, which they have been prohibited from entering, suddenly opens. She goes inside and sees a Virgin Mary statue with a snake around her neck. She sees a rocking chair facing away from her moving as if someone is in it, and she goes to investigate. When she puts her hand on the chair and looks over it she is frightened by rattlesnakes that strike out at her. She is found unconscious on the floor and dies on the way to a hospital. The doctor says she died of a heart attack, but we know it was the voodoo magic snakes that scared her to death.
We hear voodoo drums playing and see Pauline's servant Thomas with a skull candle. Then we see the second granddaughter Lorena in bed as a large snake crawls around her feet and up to her head. She wakes up and sees the snake, then passes out as the snake crawls away. Then we see what looks like her ghost leave her body, then her body gets out of the bed. She has been turned into Thomas' voodoo zombie.
In a secret underground room we see a group of people dancing. One man dances with a large snake around his shoulders. The fourth of Pauline's heir, a white man named Dr, Cunningham, is searching for Lorena and discovers the secret room. He is startled by a large snake hanging over the doorway. We see a woman tied up to a pole with a snake at her feet, then on her shoulder and later wrapped around the pole. Thomas and the snake-dancing man torment her with knives and eventually kill her. The snake doesn't seem to do much of anything except to scare people in the audience who fear snakes. Eventually Thomas and Dr. Cunningham have a sword fight with machetes, which is much more exciting than any of the snake scenes, but this is not a web page about machete fights in movies (I'd look at that site) so you'll have to watch it to see how it turns out. Spoiler alert: the good guys always win.
The first rattlesnake we see in the plant arrangement is a juvenile of some unknown species.
The rattlesnakes in the rocking chair are Western Diamond-backed Rattlesnakes.
The large snakes in Lorena's bedroom and at the voodoo dance party are Boa Constrictors.