THORNHILL: In the world of advertising, there is no such thing as a lie, Maggie. There is only the expedient exaggeration.
Thornhill's comment to his secretary sets up a film where expedient lying seems to be everyone's M.O. Nothing is really what it seems.
TOWNSEND: With such expert play-acting you make this very room a theater.
The room where Vandamm's holding Thornhill (or where "Townsend" is holding "Kaplan") takes the place of the theater where Thornhill was supposed to be attending a performance that same evening. The coincidence is too neat to be just coincidental; the line instead indicates just how obsessed North by Northwest is with appearances and acting.
THORNHILL: What a performance!
Thornhill can't believe his ears when he hears the woman who's pretended to be Mrs. Townsend—who he's never met before last night—claiming to be an old friend of Thornhill's instead. And as audience members we have to agree with him: there's no denying this woman's such a good liar that she's a gifted actress.
VANDAMM: When you return to New York, do say goodbye to my sister for me, and thank her for her superb performance as Mrs. Townsend.
Notice that Vandamm uses the same language to praise his sister that Thornhill had used to condemn "Mrs. Townsend" as a liar. These two guys really can't agree on anything in the film except this woman's performance. And it's telling that this is the thing they'd agree on, since both men rely on performance as the film unfolds.
VANDAMM (to Thornhill): Has anyone ever told you that you overplay your various roles rather severely, Mr. Kaplan?
The irony here is that Thornhill isn't yet acting; he's telling the truth, that he's Thornhill, not Kaplan. But in the world of North by Northwest, truth and lies are hard to tell apart. In the spy biz, everyone's lying and assumes the other guy is too. Eventually, Thornhill will have to play Kaplan—and "play dead" as Vandamm predicts—in order to rescue Eve.
THE PROFESSOR: We created George Kaplan.
The Prof points to the fact that fictions can acquire lives of their own. It's as if spy agents were artists: the fictional Kaplan becomes the real Thornhill, who becomes Kaplan, in order to become fully himself (i.e., his own man, no longer his mother's son, and so on). It's a beautiful narrative system that doesn't get completely sorted out until the last impostor—Eve—is revealed to be working for the feds. Whew!
THORNHILL: (to Eve): Is that a proposition?
Thornhill's surprised (and so are we) by Eve's forwardness when he first meets her. During this same conversation, Eve says, "I never discuss love on an empty stomach." This line was dubbed at the insistence of Hollywood censors: in the original version of the scene, Eve said, "I never make love on an empty stomach." (Watch her lips closely and you can see the dubbing.) Hitch also had to add the words "Mrs. Thornhill" to the dialogue to get approval for the last scene. (Click here and scroll down to "The Production Code" for the skinny.)
THORNHILL: Wouldn't it be nice if my problems and your plans were somehow connected? Then we could always stay close to each other and not have to go off in separate directions. Togetherness, you know what I mean?
Thornhill is bitter and sarcastic when he confronts Eve in her hotel room in Chicago after his return from nearly being crop-dusted to death. Since Eve was the one who sent him there, he knows she's up to no good. Still, there's an intimacy about this exchange. We're kind of invited to imagine a future together for these strangers on a train.
THORNHILL: What's wrong with men like me?
EVE: They don't believe in marriage.
THORNHILL: I've been married twice.
EVE: See what I mean?
Eve knows the score when she meets men like Thornhill with commitment issues. But we really don't know what to make of it because she's the one driving the seduction, not him. Later, we really don't know what to make of it since she betrays him to Vandamm. She's pretending to be someone who's pretending to be seductive—typical Hitchcock.
THORNHILL: If we ever get out of this alive, let's go back to New York on the train together, alright?
EVE: Is that a proposition?
THORNHILL: It's a proposal, sweetie.
Eve repeats Thornhill's question from their first extended conversation on the train, in the dining car: "Is that a proposition?" This underscores how how far they've come since that first encounter. And with his "proposal" Thornhill's already predicting the happy ending as well as satisfying the production code guys.
THORNHILL: Come along, Mrs. Thornhill.
Hitchcock wouldn't have been allowed to show his lovers climbing into bed unless they were married, and this dialogue was a last-minute addition. The film yadda-yaddas over the marriage part. One minute Eve's hanging perilously over a cliff, the next minute she's safely in the arms of Thornhill.
THE PROFESSOR: War is hell, Mr. Thornhill, even when it's a cold one.
The spy business reached its height during the Cold War era, when wars were fought with intelligence and not weapons. The CIA conducted espionage activities around the globe and kept close eyes on their Eastern Bloc counterparts. The Professor tries to keep Thornhill in the game by appealing to his sense of patriotism.
THORNHILL: We're on top of the monument.
In case you didn't catch just how close Roger and Eve get to those big presidential heads, the hero, running for his life, reminds you. A lot hinges on the dash across the great presidents' heads in North by Northwest, and the climactic chase scene's monumental backdrop underscores just how much is at stake, making the chase, too, seem monumental as well as exciting.
In the years following the film's release, the Park Service had to shoo more and more visitors out of prohibited areas of the monument. But overall, the film brought lots of great publicity to the park; tourists still ask about the film when they visit Mount Rushmore. (Source)
THE PROFESSOR: Thank you, Sergeant.
VANDAMM: That wasn't very sporting, using real bullets.
The scheming Vandamm keeps up his characteristic sarcasm to the very end. These are the last words we'll hear him say after his capture by the Professor and police, and they emphasize the sudden switch from blanks to real bullets that takes place as North by Northwest approaches its conclusion. The sergeant who takes Leonard down just in time gets to shoot a firearm that's the genuine article. Lucky for the newlyweds-to-be and the whole free world.
THORNHILL: If you fellas can't lick the Vandamms without asking girls like her to bed down with them and fly away with them and probably never come back alive, maybe you better start learning to lose a few cold wars.
This is the closest anyone in North by Northwest comes to criticizing the Cold War strategies that provide the film with its context. Here Thornhill objects to the extremes that the Professor is using to gain information. But a statement from earlier in the film has already anticipated, and pretty much defused, Thornhill's objection.
REPORTER (in the agency meeting at headquarters): C'est la guerre.
Translation: Such is war. (Think "c'est la vie": that's life.) Some of the Professor's fellow agents—and, later on, Thornhill—object to the ruthlessness of the tactics that he relies on to foil Vandamm and protect the national interest. But for the Professor and his crew it's all in a day's work when you're in the midst of a Cold War.
MRS. THORNHILL: You gentleman aren't really trying to kill my son, are you?
This is hands-down Mrs. Thornhill's most memorable line in the film, not least because it prompts several awkward minutes of laughter. In addition to being brazen, her question shows how little she respects Thornhill. She places so little faith in his story about being abducted and forced to drive drunk that she thinks she can put an end to his Plaza Hotel antics by simply asking his pursuers about it. File under: unsupportive. This is one example of why Thornhill has to break away, though he doesn't know it at first.
MRS. THORNHILL: Pay the two dollars.
Here's another line for the unsupportive file. Mrs. Thornhill has followed her son to the scene of the previous night's crime: the Townsend estate, taken over by Vandamm and his cronies, who are pretending to be the Townsends. But here as in the hotel elevator a few scenes later, Mrs. Thornhill's convinced that Roger has made up the whole story about this kidnapping. In this case, she urges him to pay the fine he's been charged for driving while intoxicated.
(FYI, "Pay the two dollars" is a line from an old vaudeville routine that roughly translates to "You can't fight city hall." We know this was 1959, but we sure hope the fine for drunk driving was more than two bucks.)
THORNHILL: (to police) That was mother.
Arrested for drunk driving, Thornhill uses his one phone call to contact his mother, who's not too thrilled to hear from him in the middle of the night. This line does important work, since it clues us into Roger's mommy issues early on. Is this why his first two wives dumped him?
THORNHILL: They've mistaken me for a man who's only five feet tall.
MRS. THORNHILL: I've always told you to stand up straight.
Here again, in George Kaplan's room in the Plaza Hotel, we get confirmation that Mrs. Thornhill refuses to treat her son like a full grown-man. "No wonder, then," the viewer's meant to think, "her son can't act his age." This is, again, why mommy dearest has to be ushered offstage.
MRS THORNHILL: Roger, will you be home for dinner?
This line, delivered while Roger's fleeing Vandamm's men, marks Mrs. Thornhill's exit from North by Northwest. Roger will talk to her on the phone from Grand Central Station, but never again will we see her or hear her voice. The film answers her question with a resounding no: he won't be home for dinner. And the whole rest of the film shows what he does instead, as if to illustrate all that's possible when you finally think for yourself.