evolution theory, absolute crap I'm sure, very horror
the notion of human sentience being the result of a partially distributed intelligence resulting from tight biointegration (think fishes with worms for tongues, kids, there's never one real example of anything ever) with a arthropod parasite co-ancestor that eventually also integrated into our reproduction, and so tentacle stomachs from hell start tearing out of people suddenly a la alien when they're of certain ages
re: evolution theory, absolute crap I'm sure, very horror
This sort of thing is a part of nature, and a part of our shared evolutionary history: we know that mitochondria are descendants of ancient symbiotic bacteria related to existing bacterial parasites, and that substantial parts of our genome originate from ancient viruses co-opted into functional roles.
There are actually worms with their nutrition and excretion systems entirely replaced by symbiotic bacteria.
re: evolution theory, absolute crap I'm sure, very horror
(this idea brought to you by the also horrifying thought that parasites in general but tapeworms particularly might be slowly adapting to eventually replicate sections of our gastrointestinal systems)