It's a Jan Svankmajer short film based on "The Pit and the Pendulum" by Edgar Allan Poe and "A Torture by Hope" by Auguste Villiers de L'Isle-Adam. Both of those are about the tortures of the Spanish Inquisition, so you can see why the Czech Communist authorities took a dim view and banned the film.
I'm sure you'll have some idea of what's involved in the Poe story, even if only by cultural osmosis. The title's a big clue. We begin with some poor bugger strapped to a table underneath a slowly descending pendulum with a razor edge. When the pendulum reaches the table, it'll cut its victim in half. Never one to do anything by halves, of course Svankmajer built a real pendulum and stuck an actor underneath it. It's real. It's bloody big. It'll make you nervous. Real rats are running around, although Svankmajer uses stop-motion animation for the one that gets lured under the blade and sliced open.
What's interesting here is Svankmajer's fidelity. He's drawn Father Time (i.e. a dirty great skeleton) on the ceiling, just like Poe. The rope-chewing rats are just like Poe.
You'll be less familiar with the next trial, which involves a Bosch-like vision of Hell with clockwork animated demons biting off their naked victims' heads. This is lurid, but it's also just interior decor. That's the Spanish Inquisition for you. What makes it a menace to life and limb is the knives and flames.
You might not be as familiar with Auguste Villiers de L'Isle-Adam (1838-1889). I wasn't, but I've looked him up. He was an impoverished French writer from an aristocratic family who was most influenced by Poe and Baudelaire. A Torture by Hope is very short and a good deal more readable than Poe, probably because the story I read has been translated into English and Poe tragically hasn't yet been. It's also pretty good and supplies Svankmajer's film with its evil punchline.
This is a simple film. It's only surrealist if you think it counts that it's portraying a religious medieval mindset, although in fairness Svankmajer loves freaky old stuff and ancient forms of storytelling (his puppet films, Faust, Don Juan, Castle of Otranto, The Ossuary). Anyway, this film doesn't need interpretation. Torture with way too much imagination is taking place in a grim, underground world of ancient brickwork. It's in black-and-white, as is right and proper. It's evil. Recommended.