system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When I have a runny nose, why only left/right side is really "runny" and not both of them?
gpt
Because only one of our nostrils is active at any given time.  It switches about once every 4 hours.   The other side isn't breathing so the mucus isn't being "pumped" out, but you will notice, when your nostrils "change guard" the other side will quickly become runny.