The microwave light had come on and the fan was running.
Only no one had touched it.
I shrieked, unplugged it, and later plugged it back in. It started up again. The turntable wasn't rotating. Just the light going on and the fan running. It stopped when I opened the door, but started back up again once I closed it.
The good news: Emerson is sending me another microwave for free. All I have to do is cut off the cord (do you think I need to use a wooden stake and wear garlic or a large cross around me neck?) and send it and the manual back to Emerson.
The bad news: It sounds like they're going to send me the same model.