[Lawtan]

...I sort of found a whole fount of disturbing real-life stories, so not too surprised. More worried about why they do that...

(Stories of morbid curiosity below)

There are...or were...apparently people who got off on giving others illnesses. Terminal. Sexual. What have you. As in not the fictional parasite take-over-the-world Men-in-Black thing, but a mental guy infected with AIDS trying to infect others.

Then we have a restaurant for the wealthy "we've done everything else" class...who allows clients to rape the animal they well later cook and eat. And yes, bestiality is essentially raping animals. It is not uncommon that those animals become fearful and hostile afterwards.

Then we have one of the reasons euthanasia (both animal and human) is regulated. Earlier on, especially with animals in early animal shelters, vets registered to administer it would do it in a hurry - either to maximize profit or get beck to their main part of the job. However, early drugs for euthanasia worked similar to overdoses. When administered too quick, the animals would pass out, appear dead, and then on the way to mass burial wake up and puke themselves to death.

Oh, and we used to have that problem during the late 1800's/early 1900's. Oftentimes if an illegal immigrant employee in a meat factory died, they'd be disposed of as part of the processed meat. That and other terrible conditions were why laws were passed to inspect such places and all...given, the processing itself makes it rather hard to tell meats apart.

Then there are people dying in water supplies, or fungi getting into the ventilation systems...

...I could go into the stuff with human trafficking, but I'll leave that here...

Closing off with this guy:
Arthropelura
which likely inspired this thing
Tomb Stalker