system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What causes the feeling of butterflies in one's stomach when they feel nervous/excited?
gpt
Part of your flight of fight response is to prepare your body for action in cases when you think something dangerous is about to happen.  Part of that response is to decrease blood flow to non-vital areas of the body, so that blood can flood into your muscles, where it will be more useful.  Digestion is one of the areas that isn't real important in the middle of a fight, and the body decreasing the blood flow to the stomach is what gives you the butterflies in the stomach feeling.