system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 what are "butterflies in my stomach?"

What am I feeling when I'm nervous and get "butterflies" in my stomach? Why does this happen only when I'm nervous/worried?
gpt
When you are nervous, you body goes into 'fight or flight' mode, and basically prepares the body to either do a runner or smack someone. It does this by diverting the blood in your system to your arms and legs. The butterflies you feel is just the blood being diverted away from the stomach, together with the high level of adrenaline you are experiencing which raises your heart rate,  and your breathing which heightens your sensitivity to changes internally.