Hawkeye and Trapper are leaving the swamp. If you look through the tent, you will see nobody behind it. When Hawkeye and Trapper are outside, suddenly a soldier is working in front of the tent.
Frank: (reading the narration) Every red-blooded American knows if he is wounded, he will be in the strong, capable hands of a Yankee Doodle Doctor.
Trapper: (laughing) A Yankee Doodle Doctor?!
Hawkeye: (singing) Stuck a feather in his nurse...
(joined by Trapper) ...And called her Macaroni!
Frank: Why, for a while there it was a toss-up whether I'd be a doctor or an actor.
Hawkeye: What finally happened?
Hawkeye: Who are you calling a you-you?
Hawkeye: Gee, I was sitting around minding my own business, when all of a sudden...poof! A star is born!
Hawkeye: (to a nurse, as the Groucho-inspired doctor in the film) Wanna go inside the oxygen tent for some heavy breathing?
(The ending of the film.)
Hawkeye: Three hours ago, this man was in a battle. Two hours ago we operated on him. He's got a fifty-fifty chance. We win some, we lose some. That's what it's all about... no promises, no guaranteed survival... no 'saints in surgical garb.' Our willingness, our experience, our technique are not enough. Guns, bombs, and anti-personnel mines have more power to take life than we have to preserve it. Not a very happy ending for a movie. But then, no war is a movie.
Hawkeye says (about Trapper), "I promised Fred I'd never dance with anyone but him." This is probably a reference to actor Fred Astaire who sang and danced very well in his movies. Does this make Hawkeye his partner, Ginger Rogers?
When Lt. Bricker asks Hawkeye if he's done any acting, Hawkeye starts imitating James Cagney and saying, "Why you, you dirty rat ..."
The title "Yankee Doodle Doctor" alludes to the title of the song "Yankee Doodle Dandy" by George M. Cohen