We have observed that the bulb can burn out after 10 seconds or more. This demo can also be used to show what happens when a microwave oven is set to cook on low power. Then on again, then off, and so on. The microwave generator is simply turned on and off to create an average power over time. Thanks to Mark Wexler.
Metals surrounded by oxygen and other combustibles can ignite and be destroyed.
A poptart in its package is a good example. The shiny wrapper is made of mylar plastic coated with a very thin layer of aluminum. The aluminum is put there so that gases cannot easily pass through the membrane, keeping the food fresh longer. The aluminum layer is, however, a conductor of electricity and will heat up when subjected to microwaves, just like the light bulb filament. The result is a series of spectacular blue sparks as the metal is heated up so hot that it evaporates.