Apparently the story goes like this...
Casey wanted to make a cup of hot apple cider. So she filled a cup with water and put it in the microwave to heat. After turning it on, it caught on fire. She ran upstairs, yelling "DAD DAD DAD! THE MICROWAVE IS ON FIRE!!!!!"
He jumped downstairs, opened it up, blew out the remaining sparks... and then explained carefully to ALLLL the children that we don't put METAL CUPS in the microwave as they will self-combust.
"Oh." Casey said. "I thought that was plastic."