Dan talks about the motion picture production code, which enforced a strict moral policy on all film in the early days of Hollywood.
Sources:
screen prism overview
A History
Hays, as president of the MPAA (MPPDA at the time), vowing to clean up the moral tone in film
MPPDA Archives (For “Motion Pictures and Their Censors”)
Overview of Film Censorship
McKenna’s Opinion in Mutual Film Corporation v. Industrial Commission of Ohio
The Devil's Advocate Will H. Hays and the Campaign to Make Movies Respectable
Sound on Film
Sound proof booth for filming