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xkcd #3211: Amperage
(imgs.xkcd.com)
Title text:
Oh, and do you have any tips on how to vacuum up copper that's melted into your carpet?
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3211/
I think that's the joke, especially since the alt text asks about getting melted copper off the carpet.
The comic is talking about the cords that come out of the outlet into the room melting and starting fires. The guy you responded to is talking about wires in the walls starting fires.
Ah, the good old asbestos carpets. Cozy!