premise: There are many comic tropes a comedian or group of comedians may want to employ in their set or act, but for the purpose of this extract we shall focus on the device of the call-back. A call-back is a reference made to a previous joke, in a different context: for example, a comedian may make the joke why did the chicken cross the road? To get to the other side early on in his or her set, and then later on may reference this again by telling an anecdote and saying so then I crossed the road - oh, look, theres a chicken! Strange, I could have sworn he was over there a moment ago. Though the call-back may appear to simply rely on the idea that repetition is inherently funny, it actually has several desirable effects. Firstly, it means that one joke can provide more than one laugh, as the memory of the previous joke encourages renewed chuckling, and so the original quips comic potential is increased. It also builds up a relationship between comedian and audience, as it builds up a sense of familiarity with the speaker and his or her subject matter, and this bond also may encourage more laughter - the second joke creates the same feeling as an in-joke. If used at the end of a set - as a call-back often is - it gives a sense of completion, and also may lead to the ending of the act culminating in the largest laugh. In TV, a call-back often refers to a joke made in a previous episode.
hypothesis: A call-back cannot be used in an un-comic setting.