Harold Hill and Hamilton
In The Music Man, Harold Hill's theme song is "76 Trombones," which has the same melody as Marian's song, "Goodnight, My Someone." The movie (as well as its stage version) creates a moment when the two leads alternate singing lines from their own songs, then they start singing each others' tune. This shows their connection and oneness. (You'll see that in dances in the movies as well - the two create separate patterns of movement around the floor, then they dance in unison.)
This pairing of songs reminded me of something similar in a different Broadway show.
Currently, on Broadway is a popular and critically-acclaimed show: Hamilton: The Musical, created by Lin-Manuel Miranda (Tony-winning creator of In The Heights). The story follows the life of Alexander Hamilton, the first Secretary of the Treasury in what would later be called the United States.
There is a lovely intricacy of songs and storytelling. Alexander has several songs, parts of which can be heard throughout the songs of other characters. The first one, "Alexander Hamilton," sums up his story to the age of 19. It has a throbbing bass line, hard hitting to express the young man's determination to become an influential man.
That same through line of music can be heard several scenes later in his wife's ballad, "Burn." There has been heartache in the marriage and she's burning his letters. They are as separated as two married people can be, and yet, in a subtle way, his song makes its presence known in hers. Later (as in real life) Elizabeth Schuyler Hamilton would bear her husband's legacy; she is still inextricably interwoven in his life, and he in hers.
It's a heartbreaking reminder that, for better or for worse, they are one.
Is this a constant pattern in musical storytelling, interweaving one person's song into another's? Probably. Movies have helped me to understand and appreciate subtleties in musicals.