The line in question occurs during the brief sojourn in which Clemenza and Rocco Lampone (Tom Rosqui) take the traitor, Paulie Gatto (John Martino), around New York City before whacking him as a result of his helping facilitate the attempted assassination of Don Vito Corleone. In the montage as presented in the film, Clemenza and Lampone have Gatto drive them around supposedly looking for things to bolster the war that Sonny Corleone (James Caan) is threatening as retaliation for the attempt on his father’s life, only to park near a field as Clemenza needs to relieve himself. While he does so, Lampone shoots Gatto in the back of the head. Before they depart, Clemenza instructs Lampone to “leave the gun,” the line that was written in Puzo’s novel and the film’s script.
After that, the second part of the line is the part Castellano improvised on set: “Take the cannoli.”
Like any good improv, the line is rooted in textual materials, which is undoubtedly why Coppola left it in the final cut and allowed the line to become as famous as it has. It refers to Clemenza’s established love of Italian food (as seen in the scene where he tells Al Pacino’s Michael his special sauce recipe) and continues the general theme of saturating the film and the characters in Italian-American culture. For another, it acts as a payoff to a line spoken by Clemenza’s wife (played by Castellano’s real-life girlfriend, Ardell Sheridan) just a few moments earlier, in which she instructs Clemenza to pick up a cannoli for her.
Furthermore, the line doubles as a punchline to a moment that was shot but deleted from the final cut of the film. As originally conceived, Clemenza was to take Gatto for a ride both literally and figuratively, letting the traitor sweat it out while throwing him off-balance. As part of this, Clemenza orders Paulie to drive to an Italian restaurant, ostensibly so he can contact Sonny for more information. Instead, Clemenza goes inside and sits down to a luxurious meal, making sure to take a cannoli to go after he’s done.