The look Fëanáro gives him could best be described as an unholy combination of disgust and perplexity.

"Why in the name of--" He frowns, eyes darkening, cutting himself off. "Why would they do such a thing? If you have not a word for a thing, it would seem simpler to create one, that it be better integrated to the whole of the tongue seamlessly, rather than cut, and pick, and paste a nonsensical hodgepodge--"

He has begun ranting, rising to his feet and pacing as he does, the vital flame burning in him becoming evident. His force of personality is almost a palpable thing, radiating out like heat or light, and Clark has a very narrow window of opportunity, if he wants to cut the greatest of the Ñoldor off from his tangent.