"What I just killed?"
Rather than focus on the fact that the machine was supposed to be a weapon for humanity, Gus instead was captured by the use of that single word. Perhaps it was just something that he was thinking about in the wrong way, but to him the use of the word killed was something that should have been used only for something that was a living creature. And while that thing did have some parts of an animal of some kind, it was a far cry from being able to be called a living creature.
"Yes," she responded. "You do realise what you've just done, don't you?"
"I don't mean that. Why killed? That thing wasn't alive, so why that word exactly?"
She paused for a minute before speaking again, being incredibly careful not to reveal too much information to Gus.