And now for some light reading from uncyclopedia:
The speed of light in a medium has never been measured because mediums claim this would cause
quantum disentanglement and kill their psychic powers, much like
Schrodinger's cat. There are, however, secret societies which aim to do just this. They have been foresighted by the Mediums already.
To detect this simply set your microwave to medium and run after the microwaves as they come out.