Originally Posted by bevischief
I just leave the knife in it to keep it from blowing up and making a mess.
Actually, metal in the microwave isn't necessarily damaging in many cases. The magnetron that creates the microwave rays can't really be hurt by it. The problem is when the metal gets in just the right position, it has the possibility of acting like an antenna which focuses the microwave rays and can arc and possibly ignite something else. It just depends on how much the microwaves are dispersed around in the cage, and what type of materials happen to be in the sweet spot, and whether they're moving around. But there are many ways you can safely have metal in a microwave. Some foods actually have a small bit of metal in the packaging and sometimes that is actually intended to focus the microwaves just a little bit.