system
Given the following post, respond as if you're commenting on Reddit:
human
How can some animals "smell" fear?

I'm sure you've all heard it before, but how do you scientifically explain it?
gpt
They don't. Most mammals have good eyesight and are very good at reading body language, and that's what they're responding to. Cringing, backing away, jerky movements, high-pitched noises, and certain eye movements are indicative of fear/distress in a lot of mammals (and more importantly, their prey).