system
Given the following post, respond as if you're commenting on Reddit:
human
How do flash grenades work?

What causes the flash, as well as the loud noise?
gpt
Usually a reaction between a metal (e.g. Magnesium) and an oxidiser (e.g. ammonium perchlorate) . Basically a small explosion, but with the results focused on light and sound rather than concussive force. If you've ever burned magnesium in school, basically the badass version of that.