Groundbreaking comedian Steve Martin, who recently published his memoir Born Standing Up, has a lengthy piece in Smithsonian on how he became funny. It's a delight to read someone so smart and hysterical talk about how he "got his act together" in the late 1960s and early 1970s by discovering what makes people laugh. From the article:
In a college psychology class, I had read a treatise on comedy explaining that a laugh was formed when the storyteller created tension, then, with the punch line, released it. I didn't quite get this concept, nor do I still, but it stayed with me and eventually sparked my second wave of insights. With conventional joke telling, there's a moment when the comedian delivers the punch line, and the audience knows it's the punch line, and their response ranges from polite to uproarious. What bothered me about this formula was the nature of the laugh it inspired, a vocal acknowledgment that a joke had been told, like automatic applause at the end of a song.
A skillful comedian could coax a laugh with tiny indicators such as a vocal tic (Bob Hope's "But I wanna tell ya") or even a slight body shift. Jack E. Leonard used to punctuate jokes by slapping his stomach with his hand. One night, watching him on "The Tonight Show," I noticed that several of his punch lines had been unintelligible, and the audience had actually laughed at nothing but the cue of his hand slap.
These notions stayed with me until they formed an idea that revolutionized my comic direction: What if there were no punch lines? What if there were no indicators? What if I created tension and never released it? What if I headed for a climax, but all I delivered was an anticlimax? What would the audience do with all that tension? Theoretically, it would have to come out sometime. But if I kept denying them the formality of a punch line, the audience would eventually pick their own place to laugh, essentially out of desperation. This type of laugh seemed stronger to me, as they would be laughing at something they chose, rather than being told exactly when to laugh.