Admit it: you were pronouncing the word “Smaug” — the name of the Hobbit dragon, the one who’s in the subtitle of the upcoming movie installation — as “smog.”
Observant watchers of The Hobbit: The Desolation of Smaug — or just its trailers, as seen here, since the movie’s not actually out till Dec. 13 — will have noticed that either they themselves are saying the word wrong, or the movie is. In case you couldn’t guess (given that a movie into which hundreds of millions of dollars are being poured probably included in that budget someone to check the pronunciation of such words): you’re the one who’s wrong.
As Tolkien himself made clear in Appendix E of the Lord of the Rings trilogy:
All these diphthongs [in the books] were falling diphthongs, that is stressed on the first element, and composed of the simple vowels run together. Thus ai, ei, oi, ui are intended to be pronounced respectively as the vowels in English rye (not ray), grey, boy, ruin: and au (aw) as in loud, how and not as in laud, haw. [Emphasis added]
But don’t be ashamed to admit your mistake; even totally die-hard Tolkien fans have been there too. As the author of the Ask About Middle Earth tumblr blog points out, the 1970s animated Hobbit said it wrong, and non-English translations often write it out wrong too. But, thanks to Peter Jackson et al, the world will never again dip(phthong) into shaky pronunciation territory.