Sentence:  WOOSTER: If you ask me, art is responsible for most of the trouble in the world./ JEEVES: An interesting theory, sir. Would you care to <WSD>expatiate</WSD> upon it?/ WOOSTER: As a matter of fact, no, Jeeves. The thought just occurred to me, as thoughts do./ JEEVES: Very good, sir. 
Meaning of the word marked with <WSD> tags:  To write or speak at length; to be copious in argument or discussion.