Smaugs clever question(the catch)

Do you mean in ch 12?

Bilbo has returned to the cave and though he is on his guard, he riddles and discusses various topics with Smaug.

You have nice manners for a thief and a liar," said the dragon. "You seem familiar with my name, but I don't seem to remember smelling you before. Who are you and where do you come from, may I ask?"

"You may indeed! I come from under the hill, and under hills and over the hills my paths led. And through the air, I am he that walks unseen." "So I can well believe," said Smaug, "but that is hardly our usual name." "I am the clue-finder, the web-cutter, the stinging fly. I as chosen for the lucky number." Ch.12