Keira's guitar playing
...that continuous C chord in all the songs, and how it remained unpressed to the fretboard.
Considering all the riding, fighting and fencing she had to learn for the Pirates, I really think she could have bothered to learn a couple of chords, and how to change them.
Nice movie, though.
More subdued than I would have expected from a run-of-the-mill-looking music-themed indie romcomdrama.