So, hear me out. Imagine a regular poison. Yes, it does the job, but it's obvious, detectable via an autopsy, and suspicious. But, what if there was a poison that didn't directly kill the victim, but caused them to have a slow craving for, say water. They slowly feel thirsty and increase their water intake over the course of a month, ending in them dying due to low sodium levels (water poisoning). It would look like an unfortunate accident to the coroner. And the remaining poison won't be checked for, since why try to look for a probably-nonexistent poison when the cause of death is blindingly obvious? I propose calling it "ThirstTrap™"