I'm getting interesting results just by googling for academic work with names like "neuroscience of fear."
E.g. https://ajp.psychiatryonline.org/doi/10.1176/appi.ajp.2016.16030353
I interpret this question as seeking a list of scary things like snakes, spiders and heights. Is that what you're looking for?
Hey there! Thanks for your reply! I was actually wondering what fundamentally makes things scary, not things that are already scary. I take it that there is none?
Not that I know of—at least on this website. That being the case, here are my thoughts.
Fear is an evolutionary adaptation to avoid danger. Some things like snakes, spiders, heights, darkness, the unknown, social exclusion, people who are a little off and large charging animals are scary because evolution has had plenty of time to evolve mechanisms to recognize them. You can also learn fears. For example, guns are scary even though there is no evolutionarily programmed fear of guns. We learn to fear guns. You can unlearn fears too, via (de)conditioning.
The answer to "what fundamentally makes things scary" is "evolution, as manifested in the current environment". However, this is just one perspective. You could alternatively look at it in neurological terms and point to specific brain regions like the amygdala or look at it in sociological terms and examine what different cultures teach their people to fear. (For example, I would not be surprised if New Guinean hunter-gatherers feared walking side by side because doing so I'm the jungle is dangerous.
The question "What causes ?" has many answers, depending on which perspective you're attacking the problem from.