- Let's face it — trying to single out funny moments from Duck Soup is impossible. The movie is one long Crowning Moment Of Funny from five minutes in when Firefly first enters to the fadeout at the end.
- Groucho's favorite line in the film was, "Remember, you're fighting for this woman's honor, which is probably more than she ever did!"
- The mirror sequence.
- The trial.
- "To War!"
- The encounter with the lemonade vendor.
- Especially this exchange:
Vendor: I'll teach you to kick me!
Chicolini: You don't have to teach me, I know how!
(to prove his point, he kicks him)
- Both times Firefly gets the ambassador to call him an upstart.
- The motorcycle and sidecar running gag. The first two times Groucho gets in 'his Excellency's car!', his drive Harpo would go off, leaving the sidecar behind. The third time, Groucho gets wise. ("Oh no. You can only fool a Firefly twice. This time you get in the sidecar.") While the motorcycle remains still, Harpo in the sidecar rides off.
Rufus T. Firefly: This is the only way to travel.
- The whole bit where Groucho makes Chico Secretary of War, from start ("You want to be a public nuisance?""Sure! How much does the job pay?") to end with Harpo showing off his tattoo's to Groucho ("Well, I know one thing. I bet you don't have a picture of my grandfather." Harpo starts to remove clothes.)
- Chicolini and Pinky's introduction. To show Trentino what brilliant spies they are, they walk into his office wearing ridiculous-looking Paper Thin Disguises—Pinky even walks in backwards, wearing a fake beard and a pair of hypno-glasses on the back of his head. Trentino just stares at them dumbfounded. Then they throw off their disguises, and Chicolini proudly yells, "We fool you good, eh?"
- Trentino gets a telegram - Pinky intercepts it, looks it over, furiously wads it up and throws it to the floor. Chicolini: "He gets mad 'cause he can't read!"
- The first conversation Rufus has with Mrs. Teasdale:
Mrs. Teasdale: The future of Fredonia rests upon your shoulders. Promise me you'll follow in the footsteps of my husband.
Mrs. Teasdale: (sadly) Why, he's dead.
Rufus: I'll bet he's just using that as an excuse.
Mrs. Teasdale: I was with him until the very end.
Rufus: No wonder he passed away.
Mrs. Teasdale: I held him in my arms and kissed him.
Rufus: Oh I see, then it was murder! Will you marry me? Did he leave you any money? Answer the second question first.
Mrs. Teasdale: He left me his entire fortune!
- When Freedonia is bombed, Groucho manages to get a giant vase stuck over his head. Harpo's idea of helping is to draw Groucho's face on the outside of the vase.
- So how do they get the vase off of Groucho's head? With Dynamite.
Rufus: (post-explosion) Any mail for me while I was gone?
- When Chico is asked to go out into the war zone:
Chicolini: I wouldn't go out there unless I was in one of those big iron things, go up and down like this... What do you call-a those things?
Chicolini: You're welcome!
- "JOIN THE ARMY AND SEE THE NAVY"
- During Chicolini's trial (which was full of objections, from both sides):
Rufus: Look at Chicolini. He sits there alone, an abject figure—
Chicolini: I abject!