Even when music is intended to deceive, it needs to be captioned if it’s instrumental to the genre.
Just because words are spoken doesn’t mean they need to be captioned.
What would closed captions be like if diehard fans were in charge of captioning their favorite shows?
When music lyrics are instrumental to a film’s plot, they need to be captioned. It’s as simple as that. If captioners are responsible for captioning all significant sounds, then any sound that’s instrumental to the plot needs to be captioned.
In this example from Twilight, captioned music lyrics draw meaning out of hiding as the backchannel breaks through into the viewer’s consciousness.