I have this problem occasionally. "Fiat" - car brand, verb, whatever - has been reliably putting The Beatles into my head. "Quo vadis?" takes me straight to Peter Sarstedt (although until I looked it up just now, I couldn't've told you who wrote or sang the song).
Fortunately, Doyle doesn't provide the spellwords for most of the rest of the spells used in the book, so I finished it without any further earworms.
