Then Bilbo fled [with the cup]. But the dragon did not wake – not yet – but shifted into other dreams of greed and violence, lying there in his stolen hall while the little hobbit toiled back up the long tunnel. His heart was beating and a more fevered shaking was in his legs than when he was going down, but still he clutched the cup, and his chief thought was: "I've done it! This will show them. 'More like a grocer than a burglar' indeed! Well, we'll hear no more of that." (12.17)

Dragons may not have much real use for all their wealth, but they know it to an ounce as a rule, especially after long possession; and Smaug was no exception. He had passed from an uneasy dream (in which a warrior, altogether insignificant in size but provided with a bitter sword and great courage, figured most unpleasantly) to a doze, and from a doze to wide waking. There was a breath of strange air in his cave. Could there be a draught from that little hole? He had never felt quite happy about it, though it was so small, and now he glared at it in suspicion and wondered why he had never blocked it up. (12.20)

"I suppose you got a fair price for that cup last night?" [Smaug] went on. "Come now, did you? Nothing at all! Well, that's just like [dwarves]. And I suppose they are skulking outside, and your job is to do all the dangerous work and get what you can when I'm not looking – for them? And you will get a fair share? Don't you believe it! If you get off alive, you will be lucky."

Bilbo was now beginning to feel really uncomfortable. Whenever Smaug's roving eye, seeking for him in the shadows, flashed across him, he trembled, and an unaccountable desire seized hold of him to rush out and reveal himself and tell all the truth to Smaug. In fact he was in grievous danger of coming under the dragon-spell. (12.62-3)