I don’t have a microwave oven, but I do have this big clock that can cook things.

The guy who did the video has a blog, and from that I’m a little surprised at some of the commentary in the video.

The absorption by the “salty water” isn’t correct — water isn’t absorbing the microwaves because it’s salty; it’s a polar molecule and will respond to the oscillating electric field all by itself. Ions would do this too, so having a dissolved salt probably doesn’t hurt or even helps, but distilled water will absorb microwaves and heat up. This is immediately followed by “turns the microwaves into heat,” which treats heat like a substance. The water is heated, but does not contain heat.

You also can’t see steam coming out of the glass, because you can’t see steam — it’s the vapor phase of water, and is not visible. What you can see are small water droplets, after the vapor has begun to coalesce. Yeah, I know that steam is used colloquially like this, but I expect better of a scientist.