I was trying to come up with ways to kill him, put bluntly. I sort of looked at him and said, well? What can you possibly do to a boy who's become an extraordinarily strange predatory alien superorganism? And I realized it's extremely difficult to damage him by any normal means. Literally nothing a sane person could try to do to kill him is going to work, realistically considering his capabilities, his limits, and what people would try given such a thing.

So he's harmed with extreme temperatures, I settle on.

So now I'm stuck with the shot of someone shoving the nozzle of a fire extinguisher down his throat. Great. Just fantastic.