Just found this in an unrelated context:

How to Use a Microwave Without Summoning Satan

Does this mean if I use a lower wattage, say, thawing some food, that I will only get a lesser demon?

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.... it might explain how diabolical some of the ready-meals are.

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Well, actually, you get the same demon but for less of the time.

Microwaves reduce their power by running intermittently.

At full power the demon is summoned, and then banished by the "bing" at the end.

At lower power settings the demon is summoned then banished a few times a second. This annoys the demon considerably and is therefore a much greater risk.

Go safely when you cook, folks.