Actually, Cecil, it’s no big deal when you microwave marshmallows, but it is kinda cool.
Just take a normal bowl, toss in 3 marshmallows (mine were old and hardened, so this may vary,) and set the microwave for about a minute.
WATCH THEM, THOUGH.
They’ll just sit still for a few seconds, then they’ll puff out and fill the bowl. At this point, just stop the microwave. No harm done, and the bowl’s easy to clean.
(BTW, I’ve seen pages that tell how to make slices of bread explode into fireballs, how to ignite toothpicks, and even how to light up neon tubes with a microwave… creepy.)