So much of Sondheim's lyrics come together once you think of him as a guy who loves to solve puzzles. Loves them so much he makes them up to challenge himself. Starting with strict insistence on perfect rhyme and matching syllable stress to the music, and then adding bespoke rules per show or song. The 3-beat meters throughout A Little Night Music, the dialect historical detail of Pacific Overtures, etc. It fits with the stories of his murder mystery parties, which sound more like a cross between ARGs and escape rooms before either name was coined, and writing The Last of Sheba.

And that's why I think his favorite songs were the ones that move characters and time through a whole short play. Numbers like Chrysanthemum Tea, Opening Doors, even Simple from Anyone Can Whistle, are the most complex puzzles he set himself; like solving a sudoku inside a Rubik's cube by using a thesaurus.