A one-of-a kind scent, I’m sure!  This tells us about the refinement of Smaug’s olfactory sense and the distance of Lonely Mountain from The Shire.

• 12.062 that there was one smell he could not make out at all, hobbit-smell;

Although “Hobbit” is listed in OED – and an invention of Tolkien’s – no hyphenated forms are.

“hobbit, n.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/87449. Accessed 14 September 2017.