system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly happens when a person twitches?

Does it have to be set off by something? If so are the triggers often similar amongst those who do twitch?
gpt
Twitching is due to something called muscle fasciculation, which is basically a small contraction. Damaged or stimulated nerves can cause twitching. A few common reasons for minor, benign twitching might include things like stress, anxiety, lack of sleep, exercising, nutritional deficiencies, too much caffeine, or a bad reaction to drugs (stimulants, estrogen, etc.). Twitching can also be due to more serious diseases, like Lou Gehrig’s disease (ALS).