system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do people habitually shake/bounce their legs repetitively while sitting?
gpt
Sitting compresses the blood vessels in your legs, so they don't get enough oxygen (this causes the tingly feeling when your legs "fall asleep"). So your brain tries to improve circulation by telling the legs to move. This is why people with iron deficiency usually have restless legs.