I came across an outtake track of Glenn Gould's historic 1955 Goldberg Variations recording session. On it you hear various studio chatter and joke cracking and mumbling and false starts and cursing.
Near the end of the track, Gould springs a heck of a musical gem, and political commentary by essentially "remixing" "The Star Spangled Banner" and "God Save the King" in real time on the piano.
His explanation is as interesting as the performance of it:
"I figured out that by leaving out the repeats in The Star Spangled Banner and starting your entry at the 13th bar of God Save The King, and then playing God Save The King over again and altering the harmony of the second half of The King to modulate to the supertonic region, it has the most marvelous effect. Listen to this..."
The intellectual complexity of achieving this is pretty stunning.
One of the things Gould's 1955 Goldberg variations recording is famous for is the fact that Gould mumbles and hums his way though it, and he *insisted* on leaving them in the final product. These could be interpreted as personal scribbles or what not. Or subvocalization; something we do when we need to glue several layers of complex data together.