You've already marveled at Fantastic Planet, the demented 1973 French film about giant blue people holding tiny humans hostage. But have you seen Les Escargots, the 1965 giant snail movie by the same creator?
Warning: The video may be a bit NSFW, despite being on Youtube.
In Les Escargots, which is presented in its entirety above, a gardener is trying to make his lettuces and things grow — and then he realizes that his own tears make them grow faster than anything else. He's a sad man, so it's no trouble for him to shed tears on his vegetables on a fairly regular basis. Unfortunately, his tears also make the snails in his garden grow as well — and they become massive, powerful creatures that go on to attack a nearby city, pulling half-naked people out of their homes and tugging them into their snail shells. And finally destroying all the buildings with their unstoppable snail power.
The final moments of the film hint at a terrifying sequel — that sadly never arrived.
This film, along with Fantastic Planet, is the work of Roland Torpor, "the modern enfant terrible of French art and letters." Novelist Dennis Cooper has a huge compilation of info about Torpor over at his blog, including some of his cartoons — which are definitely somewhat NSFW. Torpor was heavily influenced by the surrealists, and he co-founded the Panic Movement along with Alejandro Jodorowsky and Fernando Arrabal. Jodorowsky, of course, was the film-maker who almost made a version of Dune starring Salvador Dali.
Torpor also worked as an actor, most notably playing Renfield in Werner Herzog's Nosferatu. His final, most surreal work was the disturbing 1989 film Marquis, in which actors wearing period costumes and animal masks act out scenarios adapted from the writings of the Marquis de Sade — and the Marquis' "bodily appendage" is a puppet. I like the subtitle: "Quite exciting! There were less verbs than usual."
Warning: The video below is almost certainly NSFW: