Much of the story takes place aboard an ocean liner bound for America from Europe. Groucho, Harpo, Chico and Zeppo play four stowaways, who spend much of the journey trying to avoid the ship's captain and his first mate. During and after the journey, the four become involved with an ongoing dispute between rivaling gangsters, which the four brothers solve in their own way. Thelma Todd co-stars as the flirtatious wife of one of the thugs. Much hilarity ensues.
Like other early Marx films such as Horse Feathers and Duck Soup, Monkey Business is much more anarchic and gag-driven than later movies like A Night at the Opera, which heavily feature romance, musical numbers, and, well, plots. This was also the Brothers' first film written expressly for the screen rather than adapted from a stage play; S. J. Perelman was one of the writers.
Provides examples of:
- Artistic License – Gun Safety: Alky Briggs hands revolvers to both Groucho and Zeppo on two separate occasions. Both times he does so he immediately realizes that they are absentmindedly pointing them right at him, and grabs their hands to turn the guns aside. Don't hand weapons to people who don't know proper gun safety, somebody will get shot in the face. Joe Helton gives guns to Chico and Harpo.
- Black-and-Gray Morality: Joe Helton may be a gangster, but at least he doesn't try to hold Alky Briggs' family hostage.
- Closet Shuffle: Used by the stowaways to avoid getting caught.Lucille: What are you doing in that closet?
Groucho: Nothing — come on in!
- Comically Missing the Point:Groucho: Come here, babe, I like you.
Lucille: Oh, I shouldn't. What about my husband?
Groucho: That's alright. Maybe we can get a girl for him.
- Deliberately Distressed Damsel: Played with when Mary Helton drops a handkerchief in front of Zeppo, who pockets it and then drops one for her to pick up.
- Even Evil Has Loved Ones: Big Joe Helton is a ruthless racketeer, but he seems genuinely concerned for his daughter Mary.
- The Family for the Whole Family: The rival bootleggers, Big Joe Helton and Alky Briggs.
- Farmer's Daughter: Groucho complains that there aren't any in the barn.
- The Ghost: Maurice Chevalier is said to be on the boat, as the Marxes stole his passport and try to use it to disembark, but he never actually appears on-screen.
- Gilligan Cut: There's no actual cut, but Zeppo achieves the same effect when he tells his love interest he'll never leave her... then immediately bolts, as a ship's steward approaches.
- Have a Gay Old Time: While fleeing the ship's crew, Groucho hides in a closet in Briggs' suite. Briggs leaves, and Groucho and Briggs' wife go back and forth about Groucho hiding in the closet, and how he can't stay in there. Later, Briggs returns while the two are dancing elaborately, and unwittingly ends up dancing with Groucho, who attempts to kiss Briggs before opening his eyes and realizing the switch. It sounds like a perfect Stealth Pun on "coming out of the closet," but the phrase had no connection to homosexuality until at least the 1960s, making this merely a fantastic coincidence.
- Invisible Celebrity Guest: Maurice Chevalier is supposedly a passenger on the ocean liner, and a meeting with him leads into one of the film's most famous scenes, but the meeting takes place entirely off-screen.
- Juggling Loaded Guns: Alky Briggs hands revolvers to both Groucho and Zeppo on two separate occasions. Both times he does so he immediately realizes that they are absentmindedly pointing them right at him, and grabs their hands to turn the guns aside. Don't hand weapons to people who don't know proper gun safety, somebody will get shot in the face. Joe Helton gives guns to Chico and Harpo.
- No Name Given: None of the brothers' characters are actually named in the film. The general consensus seems to be that each brother is essentially appearing As Himself, this is supported as each of them is credited just by their first name in the credits
- Not So Above It All: Notable as one of the few times Zeppo gleefully goes along with his brothers' antics and even gets in a few zingers of his own.
- Pass the Popcorn: Groucho cheerfully stands between Alky Briggs and his wife Lucille while they have a spat, clearly enjoying the show. He even referees the argument, letting the participants know when it's their turn to speak. When the wife gets a little too angry, Groucho hands Briggs a gun, saying, "Here, big boy, you're going to need this more than I will."
- Point That Somewhere Else: Alky Briggs hands revolvers to both Groucho and Zeppo on two separate occasions. Both times, after he does so he immediately realizes that they are absentmindedly pointing them right at him, and grabs their hands to turn the guns aside.
- The Singing Mute: Implied when the unseen foursome (including mute Harpo) are heard singing barbershop from inside four barrels.
- Some of My Best Friends Are X:Emily: Oh, but you don't understand. You see, I'm not happy with my husband. He should have married some little housewife.Groucho: Madam, I resent that. Some of my best friends are housewives.
- Strongly Worded Letter: When Alky catches Groucho with his wife, Groucho's response is:"Sir, this is an outrage, breaking into a man's home! I'm not one to make idle threats, but they'll be a letter in the Times tomorrow morning."
- Tap on the Head: Both Chico and Harpo seem to be very fond of this in the final. Harpo, obviously, takes it up to eleven.
- That Syncing Feeling: The boys all try to get off the ship by claiming to be Maurice Chevalier (he was on the ship and they stole his passport). To prove they're Chevalier they sing; Harpo's got a Maurice Chevalier record on a wind-up player strapped to his back, which eventually begins to wind down.
- They Call Me MISTER Tibbs!:Briggs: Now, listen, bozo—Groucho: That's Mister Bozo to you.Briggs: Alright, Mr. Bozo.
- Took a Level in Badass: Zeppo: He spends the first half of the film running from ship security and being nervous about holding a gun. He ends the movie brawling with gangsters, and having a prolonged fight with Alky Briggs.
- Tough Room: The director told the extras in the party scene to laugh when Harpo did something funny because he was afraid the movie's audience wouldn't laugh otherwise, thinking that there was something wrong with him.
- What Happened to the Mouse?:
- Harpo infiltrates a Punch and Judy show in progress, and starts interacting with the puppets... so what happened to the puppeteer who was controlling them before he got involved? note
- While at the party towards the end Groucho starts to romance Lucille Briggs again but they are interrupted by her husband. Lucille runs away to avoid being seen and never turns up again, leaving that subplot unresolved.Briggs: Who was that, my wife?Groucho: Married for twelve years and you have to ask me?!
- "Which Restroom?" Dilemma: In one scene, Harpo stands in front of a bathroom sign that apparently reads "MEN". A guy enters then gets thrown out. Then Harpo leaves and we see that he was obscuring the "WO" in "WOMEN".
- You Watch Too Much X: Groucho says this to one of the gangsters:"Nice old piece of melodrama, kidnapping a girl. You've been reading too many dime novels."