Does Luna play the guitar alongside Lincoln and Lori by pure chance? Or did she do this on purpose to ensure that no one would hear the insults uttered by both of them?
Did Lincoln really recognize his mistake in offending Lori? Or does he just think it's unfair to offend someone who buys you another pair of goggles to make up for it?
Alternative Joke Interpretation: When Luna rocks out and censors the entirety of Lincoln and Lori's profane rants, is Luna so loud no one can hear it? Or is this just an editing trick so that the viewer of the cartoon doesn't hear it? Clyde can hear Lincoln perfectly well despite Luna's playing, suggesting the former.
