system
Given the following post, respond as if you're commenting on Reddit:
human
[Troll Hunter] How are trolls able to smell the blood of Christians?

Or perhaps the question should be, what makes a Christian's blood have a unique smell that is difficult to mask with troll stench?

It appears that people who are not Christian are generally safer around trolls than those who are. Everyone else in the documentary, the atheists and the Muslim girl, seemed to escape any preferential treatment by the trolls. It seems that there is something about Christians specifically.
gpt
I dunno. Magic, probably. But there's a rational explanation for the sunlight thing so maybe it has something to do with brain chemistry and hormones. Would be nice if we could pay some scientists to figure it out, right?

Could be an evolved trait in response to troll-slaying knights from centuries ago. Or, much scarier, they tell each other stories about it. Perhaps they remember the scent, and are still angry about all the men in bright armor with sharp swords. That would mean that if a troll hunter kills one and lets his friends get away, they might share the tale and figure out how to recognize that same scent of loneliness and depression that comes from an underpaid, overworked civil servant. What if a couple hundred years from now they'd be able to smell the blood of postmen?