The world is, as we all know, in a sad state: corrupt politicians constantly trying to diminish democracy to increase their own power; international corporations ignoring laws; mobsters taking over large parts of the economy because they can.
Now, fortunately, I have discovered I have a superpower: I can shrink myself to a few mm in size and teleport anywhere, even inside another body! And I decided to become a superhero by using my power to kill the worst of those people.
Only .. I need the deaths to look natural. The people I want to kill don't exist in a vacuum; they have friends and followers, and a death that looks unnatural might make the situation worse, not better. If the 75 year old president of Elbonia drops dead from a heart attack, people will mourn him, but if the 35 year old president dies from poisoning, the Elbonians will start a war with their neighbors because who else could have poisoned the president? Likewise, an obvious unnatural death of a drug boss will lead to a gang war, which I want to avoid. I'm a superhero, after all, not a supervillain!
So, once inside their body, how can I kill people - under the assumption that a very competent pathologist or forensic investigator will examine the body, and I want them to be convinced the cause was natural?
- Of course I could drop some toxic substance, from botulinum to an insulin overdose, but those will be detected.
- I could drop some cancerogenic substance which might not be detected anymore when the victim develops cancer, but I want them to die within hours or days, not months or years.
- Slitting open a main artery would work as well, but I'd be giving the pathologist a heck of a puzzle, and they probably wouldn't attest to a natural death.
- I might be lucky and find an aneurysm that I'd just have to punch a few times to make it break, but most people wouldn't have one I could use to begin with.
- Blocking an artery to cause a stroke would work as well, but again be puzzling at the autopsy if the victim's veins are generally in a good condition.
I need a way to kill my victims and make the investigator say something like "this is uncommon in people that age, but it happens now and then. Bad luck, but no foul play". Actually I need many different ways. If one drug boss dies of a rare cause, it's bad luck. If ten of them die, it's already suspicious, but if ten of them die of the same rare cause, nobody will believe in chance any more.
So, which ways do I have to kill those guys?
(Please, take the science-based tag with a grain of salt. Of course the whole premise of the question has nothing to do with science at all. But I'd like the answers to be based in biology/medicine; real causes of death that could undetectably be caused by messing with the inside of a body).