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.
The Hobbit - J.R.R. Tolkien