A great leap for mankind was mastering fire. Over tens of thousands of years, we not only learned how to start fires but also improved methods of heating. However, it wasn't until the last century that a now-common device appeared—the microwave oven. Why did it take so long to invent it? If you want to see how to catch electricity straight from the air, light a bulb without plugging it in, and find out why you shouldn’t cook eggs in a microwave, watch the next episode of ‘How Does It Work?’