 " Once More , with Feeling " explores changes in the relationships of the main characters , using the plot device that a demon — credited as " Sweet " but unnamed in the episode — compels the people of Sunnydale to break into song at random moments to express hidden truths . The title of the episode comes from a line sung by Sweet ; once the characters have revealed their truths and face the consequences of hearing each other 's secrets , he challenges them to " say you 're happy now , once more , with feeling " . 
