It was executive producer Douglas Petrie who first broke the news that the season would use a carnival as its primary setting. 
The official main cast for season four of American Horror Story was announced at the San Diego Comic-Con on Saturday evening, July 26th, 2014. 
Ryan Murphy revealed that AHS veteran actress Sarah Paulson would be coming back around for a fourth time, although now she would be working "double" time as she takes on the role of conjoined twins Bette and Dot. The first official photo still from the set revealed a back-shot of the twins wearing a hospital gown staring out of a window. 
Jessica Lange was one of the first cast members slated to return for season four. It was revealed by series showrunners that she would once again be taking on a leading role, this time playing a German expatriate, who is the manager and recruiter of one of the last traveling freak shows in the country. 
It was announced on the final night of PaleyFest that former The Shield and Vegas actor Michael Chiklis would be joining the cast of American Horror Story. Chiklis' character, Dell Toledo, is the former husband of Kathy Bates' character, Ethel Darling and the father of Evan Peters' character, Jimmy Darling. 
The song that Elsa Mars performs on stage, which Gloria Mott refers to as "caterwauling", is "Life on Mars?" by British pop star David Bowie. The presence of the song in this episode is anachronistic as the story is set in the late 1950s and the song was not released until 1971. It first appeared as a single and was also on the album, Hunky Dory.
Perceived blooper: Elsa Mars' rendition of "Life on Mars?" may be construed as a blooper to some as the song was not released until 1971, however its inclusion in this episode was actually intentional. Who's to say that David Bowie didn't rip the song off from Elsa?
Bette Tattler: Dear Diary. It was the glorious third of September when I was finally freed from the shadows. The future had never seemed brighter.
Dot Tattler: Dear Diary. It was a Saturday, the 3rd of September, that the world as I had known was forever doomed. The shadows that had sheltered me were banished by the blinding light of scrutiny. I knew I was about to enter the gates of Hell. But like the inescapable pull of gravity, there was nothing I could do about it.
Elsa Mars: Ladies and gentlemen. Everything you've heard is true. All that has been advertised is here, under this tent. Wonders. Curiosities. A plethora of the strange, the weird, the bizarre, the unusual! From jungles untamed to forests enchanted. From the Dark Continent to the spice-laden lands of India. Astounding mistakes of nature are gathered here for your amusement and edification. What you're about to see will astound your very senses and harrow... yes, harrow your souls.
Elsa Mars: I'll tell you who the monsters are! The people outside this tent! In your town, in all these little towns. Housewives pinched with bitterness, stupefied with boredom as they doze off in front of their laundry detergent commercials and dream of strange, erotic pleasures. They have no souls. My monsters, the ones you call depraved, they are beautiful, heroic ones. They offer their oddity to the world. They provide a laugh, or a fright, to people in need of entertainment. Everyone is living the life they chose.