system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When you feel guilty about something why do you feel something in your stomach?
gpt
The exact reason hasn't been determined because the idea of guilt is a mental thing, and we've got a long way to go to really understand definitively the brain.

That being said, think about the circumstance and only that. Let's say you are playing in the hallway and accidentally smash your grandma's vase. It's her favorite vase that she got years and years ago. They don't even make that kind any more. And you know she heard it way back in the back of the house, so you know she's coming. So what happens? You get that pain in your stomach, right?

Well let's look at it a little more simple. Let's say you're still playing around, only now it's 400,000 BC, the time of cavemen. And instead of breaking a vase, you kick a stone. The stone goes flying off and smacks right on the head of a mammoth. And he's not happy about that either. Now clearly, you know you'll want to run, that's the smart thing to do (and you may want to fight, that's... smart... too). It's called fight or flight. But *right* before it kicks in, right before you jump into action, you tighten your abs. And that clench that you feel is right around your stomach. That's where the important stuff is that your bones don't cover. (This area is specifically called the Celiac plexus, or Solar plexus. But you don't need to know that for this lesson.)

So every time you find yourself in a panicky situation, your body has that reaction of "I've gotta run" or "Looks like it's face-punching time," instinctively, before you really think about it. But when we do think about it, we can tell our body "It's okay, it's not go time" and control ourselves. That's one of the wonders of evolution. You don't see everyone running around with staplers and kitchen knives because a tire blew out. The result of that control, the understanding that breaking a vase isn't a one-way ticket to Murdertown, is that clench in your stomach. Another way to look at this last point is: we've evolved out of the need for the appendix, but it's still there.

**TL;DR You feel something in your stomach when you're guilty because our ancestors had to stab Mammoths.**