system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What happens when you feel a muscle twitch, but it doesn't appear to twitch outwardly, or when you touch that area of the body?

Surely everyone's had that weird phenomenon, you feel like a tiny thread of muscle in your eyebrow is just twitching. You feel like if you looked in a mirror right now, your eyebrows would be twerking around like in that Cadbury ad - but you go and look and nothing, your skin is completely flat, nothing twitches, but you can feel it. You touch it, and the skin and muscle underneath it doesn't move, your finger feels nothing, but you FEEL it.

It's like my brain is playing a trick on me, and I want to know why. Is it just one random neuron that's dying, or having a neuronal seizure or something? Is it psychosomatic?

EDIT: Should probably clarify that this happens extremely rarely, and I'm not concerned about it in any way at all, it happens to people I know sometimes as well, it's just a weird thing the body does sometimes, it's never caused anyone any concern.
gpt
You're probably feeling a muscle fasciculation. Which is just a few fibers in the muscle twitching. It's so small you won't see on a big scale, but you will be able to feel it.

Most of the time it's normal. If you've sustained a nerve injury due to trauma, the muscle can twitch as well, and you'll need to do special tests to detect those twitches.