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 women in prison movie that tried cash in on the B-movie success of The Big Doll House, released earier the same year. It even uses a few of the same actors, including Pam Greer as a vicious prison guard, and the same scanty prison uniforms and female guards in pony tails, mini skirts, and boots. Because that's how they always dress in women's prisons, isn't it?
In the snake scene, we see the four principal female prisoners in their prison cell at night. One of them sees a black snake crawl in through the barred windows. She tears a thin wooden board off her bed and uses it to pick up the snake. Then she puts the snake on a sleeping woman who she was paid to kill. The woman wakes up, screams, and throws the snake onto the floor. Her screams wake up the other women in the cell, one of whom grabs a bucket and beats the snake to death. (We see a bucket actually bashing a snake to death.) When the guards come to investigate the commotion, the fourth woman picks up the dead snake and throws it at them. Then the woman who tried to use the snake as a weapon hides her guilt by saying: "Those dumb snakes! They're all over this place."
I don't know what kind of snake it is - some kind of harmless snake from the Phillipines most likely, although it looks a little like a Nerodia species from North America. But in the movie universe, all snakes are venomous, deadly, and always want to bite and kill humans, so every one must die.