Gaslighting: When the team finally reaches america, they move beds from one room to the other to anger the detective.
Food Porn: The scene where Chico, Harpo and Ricardo finally get to eat will make any viewer seriously hungry for Italian food. Pasta with sauce, salamis, whole tomatoes, wedges of cheese, loaves of bread, and bottles of wine - all served on a single plate!
Driftwood: You're willing to pay him a thousand dollars a night just for singing? Why, you can get a phonograph record of 'Minnie the Moocher' for 75 cents." (Pause) For a buck and a quarter, you can get Minnie.
Gold Digger: Driftwood lusts after Mrs. Claypool's money, and he isn't exactly subtle or great at hiding it.
Driftwood: You see that spaghetti? Now, behind that spaghetti is none other than Herman Gottlieb, director of the New York Opera Company. Do you follow me?
Mrs. Claypool: Yes.
Driftwood: Well stop following me or I'll have you arrested!
Logical Fallacies: Half of the hilarity comes from Groucho's elaborate wordplay and mind games.
Driftwood: That woman? Do you know why I sat with her? Because she reminded me of you.
Mrs. Claypool: Really?
Driftwood: Of course, that's why I'm sitting here with you. Because you remind me of you. Your eyes, your throat, your lips! Everything about you reminds me of you. Except you. How do you account for that? (beat) If she figures that one out, she's good.
Tough Room: Driftwood gives an opening speech at the opera that in real life would have brought the house down, but the only response he gets is stony silence.
You Get What You Pay For: Drifwood overhears that Lasparri is going to be paid one thousand dollars per night and decides to skim the deal somehow. He is clueless and assumes Fiorelos is Lasparri's manager, so he is willing to pay 10 dollars per night. He learns later that he was hiring Ricardo Baroni instead. It turns out Ricardo Baroni is an excellent singer, just unknown by the public.