Interesting, I imagine the monkey they ate was one that had been driven away for abnormal behavior. Coupled with the behaviors seemingly transferring down to the novelist, I wonder if this is some sort of parasite that gets the victim to fatten itself up so that predators find it to be more appealing to eat and therefore find a new host for the parasite. And once it reaches humans, the self-made apex predators, the victims have no choice but to end things themselves, as predators are too scarce and humans wouldn't be guaranteed to eat them.