What can't you put metal in the microwave?

Question

I know what happens i'm just dont know why.

Answer 1

Metal will cause the magnatron to over heat and the oven will be ruined.

Instead of rewriting this I'll just give you the link

http://clipmarks.com/clipmark/EE260A12-A...

Answer 2

Metal is filled with free electrons. That's what makes it shiny and what makes it conduct electricity. Microwaves can shake these electrons loose, causing them to accumulate in the pointier places. The eventually accumulate enough energy to ionize the air around them.