Most comedy directors now believe that even an expertly written script can’t reliably elicit belly laughs. Nicholas Stoller, the director of Forgetting Sarah Marshall and Get Him to the Greek, both of which were substantially improvised, said, “The movies we’re trying to make, which have a hard laugh every minute, could not be made without improv.” Traditional comedies have a sleekness that calls to mind the typewriter. Consider the moment in the 1980 film Airplane! when two passengers chat before takeoff: “Nervous?” “Yes.” “First time?” “No, I’ve been nervous lots of times.” The point of improv, Apatow told me, is to make scenes feel fresh and unstudied—“to get the imagined typer out of the way.” When an improv really works, it has a skewed specificity that bears the stamp of an actor’s subconscious. In Austin Powers: International Man of Mystery, it’s the scene where a vexed Mike Myers, as Dr.. Evil, stifles his son, Scott, with a whole run of shushes: “Let me tell you a little story about a man named Sh!” Scott opens his mouth—“Sh! even before you start.” Tiny pause. “That was a preëmptive Sh!” Scott opens his mouth again—“Just know I have a whole bag of Sh! with your name on it.”
Getting the script outta the way and replacing it with the performer's subconscious makes an entirely different cake.