6. Groucho, Chico, Harpo, and Zeppo (but not Margaret Dumont) are stowaways aboard a ship. In barrels. That's about the entirety of which 1931 plot, except for some gangsters and a kidnapping at the very end?
From Quiz Marx Brothers Motion Pictures
Answer:
Monkey Business
"Monkey Business" was the first Marx Brothers film produced in Hollywood, and the first written expressly for the cinema; the previous ones were adaptations of plays. It's also the first to lack Margaret Dumont's presence.
One famous line of Groucho's is to Thelma Todd: "You're a woman who's been getting nothing but dirty breaks. Well, we can clean and tighten your brakes, but you'll have to stay in the garage all night." Unfortunately, in 1935 she was found dead in her car, engine running, inside the garage.
The Marx Brothers have no character names in this movie, but are just credited as The Stowaways. At one point concealed in barrels they sing "Sweet Adeline" in barbershop harmony. When they try to get off the ship they use a passport stolen from Maurice Chevalier (as himself), and must impersonate him. The Brothers also manage to rescue a kidnap victim (Thelma Todd) after leaving the ship. The film was based on routines the Marx Brothers perfected in the vaudeville days, and despite the lack of plot, it was a box office smash. A sequel was planned involving more gangsters and kidnapping, but after the Lindbergh baby kidnapping, the idea was scrapped.