Shortly before this film premiered, the city of Fredonia, New York, complained about the use of its name with an additional "e". The Marx Brothers' response was, "Change the name of your town, it's hurting our picture."
Groucho Marx offered the following explanation for the movie's title: "Take two turkeys, one goose, four cabbages, but no duck, and mix them together. After one taste, you'll duck soup the rest of your life."
An early draft of the script introduces Freedonia's new dictator Rufus T. Firefly as an agent for an ammunition company, which led to lots of ammunition-salesman jokes and intertwined with the movie's war theme.
According to The Marx Brothers biographer Joe Adamson, the elaborate "All God's Chillun Got Guns" musical number was mostly improvised on the set, as there is no reference to it in the movie's final script. It's likely Groucho Marx was referring to the old Negro spiritual "I got Shoes", which repeats the line "All of God's children got..." filling "a song", "a robe", "a harp", etc. Groucho just added "Guns".
Harpo Marx's character was originally called Skippy, but this was changed to Pinky after his role in Horse Feathers (1932), making him one of only two of The Marx Brothers to reuse a character name in their films (not counting when they used their own names).
Leo McCarey told Cahiers du cinema in 1967: "I don't like (Duck Soup) so much...I never chose to shoot this film. The Marx Brothers absolutely wanted me to direct them in a film. I refused. Then they got angry with the studio, broke their contract and left. Believing myself secure, I accepted the renewal of my own contract with the studio. Soon, the Marx Brothers were reconciled with (Paramount)...and I found myself in the process of directing the Marx Brothers. The most surprising thing about this film was that I succeeded in not going crazy, for I really did not want to work with them: they were completely mad."
Screenwriters Harry Ruby and Bert Kalmar were standing on the set of one day when an extra standing next to them said, "I don't know who wrote this stuff but they ought to be arrested...they should be in a different business." Kalmer, who was known as a rational and calm man, said to Ruby, "I'm going over to hit him. Who does he think he is? He's just an extra!" But before fisticuffs erupted, Kalmer and Ruby were informed that Chico Marx had paid the extra to rib the screenwriters, just for the hell of it.
Harpo Marx's character Pinky went through several name changes in pre-production. In a 1933 Paramount press-book ad, he's known as Snoopy. For a radio trailer, his character's name was changed to Skippy.
Two Paramount contract writers, Grover Jones and Kean Thompson, were both eager and willing to be assigned to the film. They were each hired at different intervals, but both had disappeared from the production after two weeks' work. They simply did not have the stamina and perseverance in dealing with The Marx Brothers.
Final film of Zeppo Marx. After the film's premiere, he quit The Marx Brothers, citing a dissatisfaction with movie acting overall, and a weariness with being the butt of jokes regarding him as the "unfunny" Marx brother.
To help sell the film to theatre exhibitors and the public, the Paramount press department featured a number of contests to get the word out about the newest The Marx Brothers laugh fest. In addition to "Name the Four Marx Sisters," there was also a proposed duck-hunting contest, in which hunters across the fruited plain would bring back their catch to be cooked in one big duck dinner, beginning with duck soup, of course. And then there was the duck parade. Just imagine, to paraphrase the Paramount press materials, after you round up four ducks (preferably from a poultry market or a farmer), dress them as the Brothers, and let them lead the parade, you, the faithful theater manager, could then create more nonstop hilarity by tying the ducks together with a long string. "The ducks will not stay in line but that will only add to the confusion and the excitement," the press materials helpfully added.