Fork Lightning

Put metal in a microwave and you get a light show. Thin, pointed objects like fork tines act as antennas — microwaves induce currents in the metal, and at sharp points the voltage concentrates enough to ionize nearby air, creating visible sparks.

Flat metal like a spoon may not spark because the current spreads out evenly. But crumpled aluminum foil has dozens of sharp points where charge builds up, producing dramatic arcing. Those sparks can damage the magnetron and the oven's interior coating, so keep metal out of the microwave.