I love the ending of that bit.. Fields just wails on Costello to the point where it really looked like it hurt Lou and he ends up in a heap in the gutter. After Abbott congratulates him for finally getting a sufficient beating, he checks the camera...

Abbott: "WHY DIDN'T YOU REMIND ME TO PUT FILM IN HERE??!!? (slaps Costello hard, then checks his own pocket) THERE IT IS RIGHT THERE ALL THE TIME!!"

If ever there were grounds for murdering another human being, that would be pretty close to being it.