I'm a huge fan of the musical Les Miserables. Oftentimes I will find myself absentmindedly singing songs from the musical while I'm doing mindless tasks like cleaning. Since certain melody phrases repeat often in the musical, sometimes I will start a song and then suddenly switch songs, even characters, mid-phrase, without skipping a beat, and often without even realizing it.
For example: Valjean: That nothing remains but the cry of my hate? The cries in the dark that nobody hears? Here where I stand at the turning of the years. If there's another way to go/ I missed it twenty long years ago (...morph...) Javert: I am the Law and the Law is not mocked! I'll spit his pity right back in his face! There is nothing on earth that we share/ It is either Valjean or Javert!
Does this phenomenon have a name? If not a specific name, is there a good word for it? I'd accept a good, descriptive phrase too.
Pretty much the same thing can happen with poetry too, especially if it is particularly rhythmic. So if there is a word or phrase for that, it might work here too.
BTW That particular example is pretty deep. If you know the musical (or even better, the novel), that those two particular songs flow together so easily is brilliant. Kudos to Alain Boublil, Claude-Michel Schonberg and Herbert Kretzmer.