Sentence:  If it proves clearly unfeasible to make the audience laugh at a thin and far-fetched joke, it is always better to change the way the joke works . . . for instance, a pun based on the speaker's taking literally some <WSD>set phrase</WSD> or metaphor with a pun based on phonetic similarity. 
Meaning of the word marked with <WSD> tags:  An idiomatic expression in general.