So there's the crux of it, why Peridot is so upset. Chidermass grits his teeth against snapping back about how she isn't the only one who thinks that way about Lambert, because that only opens the argument up to a path he's far less comfortable with. Which means he's left frowning at the gem for her outburst, pausing a few seconds in his own counter to that, rearranging what he does want to say.

Overall, that part isn't too hard. If Peridot thinks kicking someone else into danger's path for Lambert's sake would ever be seen favorably by the witcher, well... He won't even question the dragon part, though that's definitely new. Since when could that asshole turn into a dragon? But he can't even ask about it, it would only highlight how unaware of what happened during that fight he is.

Instead, what he says is, "Really? Is that what you would have done in my place?"

He changes how he stands a little here, folding his hands behind his back rather than leaving his arms crossed over his chest, and he tilts his head at Peridot while asking that. It's a curious gesture, more akin to him asking what her preference in decor might be or what she would like for breakfast, only he's asking—

"Which of his people would you have thrown away to protect him, Ms. Peridot? Who do you believe to be expendable?"