|This is a great horror movie about horror movies. The director Drew Godard said it's "a love letter to all horror cinema." If you haven't seen it you should, so I will try not to spoil it too much, but I do have to explain some of what's happening in the snake scene.
Basically, there's a group of people in white shirts and lab coats who are in control of a giant repository of monsters from horror movies that are kept in glass cubes with easy access to some elevators for when the monsters are needed. Each department at the facility is betting on which monster will attack a group of the usual stereotypical young guys and girls we always see in horror movies who are spending the weekend at a cabin in the woods. We can see the names of the monsters on a betting white board in the control room - werewolf, clowns, witches, zombies, mutants, demons, hell lord, merman, unicorn, mummy, dragon bat, vampires, dolls, the reanimated, dismemberment goblins, and more, including a giant snake. (Like giant snakes in most horror movies, this one is a CGI composite of different kinds of snakes, with large fangs on the top of its mouth, a rattle on its tail, and a hood like a cobra.)
Eventually, all the monsters escape through the elevators and start slaughtering every person they see. We see the giant snake raise up and grab an armed guard, swallowing him head first as other guards are demolished nearby. Other guards fire automatic weapons at the snake as it escapes down a hallway. Then one of the monsters throws a man off a balcony and the giant snake rears up and catches him before he hits the ground, swallowing him whole. That's the last we see of the snake, but it's only the beginning of the bloodbath.