In Firefly Episode 9, Ariel, River and Simon take a drug that puts them in a proto-comatose state.
Around 17:30, River wakes up, says something, and startles Jayne. Jayne responds "What did you say?" but never gets an answer.
What did she say?
The subtitles I have just say "[Mutters]". But I assume that Summer Glau chose some words to say, even if they didn't form a logical sentence.
I've listened over and over, and my best guess is "Copper for a King". But I could be way off.