system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - What is it that makes people contract every muscle and scream really loud when they get scared.
gpt
Instincts. Some, if not most, animals make loud noises to intimidate/scare their enemies away. Muscles contracting would store up potential energy for fight or flight. Contraction of some muscles act to make animals look bigger (eg cat arching their back or birds fluffing their feathers), this acts to intimidate the enemy as well.