In "The Dagger with Wings" by G. K. Chesterton, Dr. Boyne was talking to Father Brown after the priest said the murderer was trying to convince him to believe fake superstitions about the murder although he could have simply killed him and escaped.
“I wonder why he didn’t,” observed Boyne. “I don’t understand it; but I don’t understand anything yet. How on earth did you discover it, and what in the world did you discover?”
I can't understand how Boyne asked him about the way that he discovered "it" with, which implies that he know the thing that this "it" refer to, then asked him about this thing by what, as if he don't know it?!!
Does it mean what else?!