system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When watching a painful video (ex: a bicycle crash), why do our nerves seem to become active, as if we are feeling the pain ourselves, for a split second?

Not sure this is common but it’s not always pleasant.
gpt
2 possible reasons.

1) Humans have special kinds of neurons called mirror neurons that allow you to "feel" in a limited sense what other humans are feeling. This is helpful to build empathy and lasting relationships.

2) Our brains are also constantly learning and trying to simulate the effects of the environment on ourselves by observing other humans. For example, if you can learn to avoid a lion after seeing what happens to another human being mauled by a lion, then that's good for your survival. If you "feel" the other guy's pain, you will learn to avoid the lion in the future. So in a sense, when your brain sees a terrible accident happen it simulates the effects to some degree on your own body in order to teach itself to avoid the said danger.