system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do parts of your body involuntarily twitch/flutter repeatedly for short to medium periods of time?
gpt
As unsatisfying as this answer is, most of the time no one has any idea why it happens. There's usually no obvious physical cause, no diseases, and no tests to show that anything is wrong. And then just as randomly stops as if it'd never been there.

And that's pretty much it. Sometimes such symptoms can be caused by injury or stroke or the like, but im assuming you're not talking about those instances.