system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When you are nervous why your leg starts bouncing uncontrollably.

Pretty self explanatory really, but I would love to know, mine does it *all the time*.
gpt
When you get nervous, your body releases adrenaline. This provides a lot of extra energy. If you are just sitting there, bouncing your leg is an easy way to expel some of that energy.
Could also just be something that is unique to you that attempts to take your mind off of whatever is making you nervous.