The thing that kills them. It's apathy.
There's a formula: The higher a group of people's apathy rises before action is taken, the more horrific things will happen within that group.
It's like the law that says companies will bloat to spend budgets appointed them, only with horror.
Apathy is a form of entropy.
Squids and Tentacles are squishy, largely unknown, and thus shiver inducing. Ditto chitinous creatures, and viruses (hereafter: viruii.)
The obvious solutions to these horrors are intent, empathy, and awareness.