... So when you get stressed out, your body reacts. Even if it's not going to, it thinks something's wrong - that's why your heart might race, because your body thinks it's about to start running or fighting. I don't... know all of the biology, but I know that puts stress on other parts of your body, which is why you feel sick.

[He's... pretty sure that's right.]

Humans... I don't know about in this world, but in mine there used to be a lot of predators around. And nature takes a lot longer to take out features than to put them in. So even if humans are pretty comfortably dominant, they still have those old instincts.