When you are not sure of the answer when someone asks a question, you say, 글쎄.
가: 놓아주세요. (Please release me.) 저는 가야 해요. (I need to go.)
나: 글쎄, 할 수 없다니까. (Well, I SAID, "I can't.")
--- In this context, Nolbu was annoyed by the fact that he had to repeatedly say that he couldn't let the swallow go.
(-다니까 used when you confirm what you told someone once and say it again)