system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why doesn't the metal walls of the microwave cause sparks but most every other metal does?

Obligatory front page edit!! Thanks for the answers guys/gals!
gpt
First off, the problem that metal in a microwave causes most often is that the metal can reflect and focus microwaves into food or onto the walls, causing things to burn or melting the walls. The worst thing that can happen is the metal reflects the energy right back into where they came from, damaging the Magnetron, the thing that makes the microwaves that cook your food. The walls of the microwave do the same thing, but are designed to evenly reflect the microwaves around the microwave without reflecting them back into the magnetron. The reason you might see sparks when you place a metal object in a microwave is that metal will naturally pick up a static charge when hit with lots of energy. When this happens in a microwave, it happens with enough energy and for long enough to see the static charge overcome gaps between one area of the metal and another, causing it to arc across, creating a spark.