system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is laughing so contagious?
gpt
While there isn't 100% consensus on this, the prevailing theory is that laughter developed as a way to signal to people that a thought to be dangerous situation wasn't dangerous - someone who saw the brush move thinking their was a predator, only to see a squirrel come out would laugh to let people know there wasn't danger.  It disarmed the situation and reduced the tension of all involved.  It would then spread throughout the group so that everyone would realize that the danger was no longer present.