You’ve seen examples of how editing can turn a set of movie scenes into something completely different from what was originally intended. We've even heard stories of actors who were surprised by the finished product because what they understood of the movie when they delivered their lines was so different from what ended up in theaters. The same principle works for movie trailers, which already have a tendency to mislead by showing only the best parts -which may be the only good parts. We’re used to being misled about the quality of a film, but Cracked looks at a few cases of the audience being misled about the type of film they went to see. For example, I did not know until today that Sweeney Todd was a musical.
Don't get us wrong -- the trailer accurately sums up the plot, showcases the principal characters, and provides dialogue in a satisfactory context. However, it leaves out one key element of the movie: It's a full-fledged musical. And we're going to guess that a whole bunch of goth kids looking for a dark period slasher film were confused as shit the first time somebody broke into song.
To be fair, Sweeney Todd is an adaptation of a popular Broadway show, but the trailer's absolute refusal to even allude to a musical component is awfully suspicious.
There are five other examples of confused movie audiences who were misled by a trailer that you can read about at Cracked. -via mental_floss