system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is nerve gas, or a nerve agent? What does it do?
gpt
The other two answers are pretty good on the 'what is it?' Question, but really gloss over the horror of the 'what does it do?' question. 

Sarin, which is a fairly well known nerve agent, affects the nerves responsible for muscle contractions and causes every muscle to contract as hard as it can. The heart just flexes and stops pumping, the diaphragm contracts and pushes all the air out of the lungs, the skeletal muscles contract with so much force that bones breaking is common. The list of effects goes on. 
There are a few medicines that counteract the effects, like Atropine, but they need to be given extremely quickly to be effective. Permanent damage starts between 1 and 10 minutes after exposure.