Once in a blue moon, special characters (e.g., apostrophes) will show up as gibberish on kindle. Fortunately, that's easy to fix. In Calibre's preferences: 1) Common Options > Text and check "Smarten punctuation." 2) To make it happen automatically: Adding books > Adding actions and check "Automatically convert added books..." and "When auto-converting, convert even if the format being added..." Now any time you add a book to Calibre, it gets converted to an epub with fixed punctuation.