system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If you're not supposed to microwave metal, why are there metal racks in some microwaves?
gpt
You can microwave metal depending on it's time and shape as long as it is designed to avoid arcing. Microwaves cause localised charge to build up in the metal and in a fork for example it will try to redistribute this charge evenly which can be seen with sparks.

Basically rather than trying to educate Joe public in what metals are ok to go in the microwave it is easier to say you shouldn't use them and avoid lawsuits.