JEFF: Next Wednesday, I emerge from this plaster cocoon.
Jeff is going a little nuts in his apartment, and the cast on his leg is the perfect indication of just how vexed he is by the situation. That restlessness is his motivation to start looking out the window, which is what sets the plot in motion.
JEFF: Stop sounding stuffy. I'll take pictures from a Jeep. From a water buffalo, if necessary.
GUNNISON: You're too valuable to the magazine for us to play around with. I'll send Morgan or Lambert.
JEFF: Morgan or Lambert, that's fine. I get myself half-killed for you, and you reward me by stealing my assignments.
GUNNISON: I didn't ask you to stand in the middle of that automobile race track.
JEFF: You asked for something dramatically different! You got it!
GUNNISON: So did you. Goodbye, Jeff.
This exchange clues us in to what a risk-taker Jeff has been. Jeff is so bored that he's still willing to take some risks to get back into the action. Spying on the neighbors seems like a harmless activity to him, but it ends up being way more dangerous than he counted on.
JEFF: If you don't pull me out of this swamp of boredom, I'm going to do something drastic.
GUNNISON: Like what?
JEFF: Like what? I'm going to get married. Then I'll never be able to go anywhere.
This is an interesting combination of Jeff's overwhelming irritation at being stuck and his disdain for getting married. It pretty much sounds like he considers the one indistinguishable from the other. They're both traps.
STELLA: I can smell trouble right here in this apartment.
Stella has got the right mixture of insight and audacity to make a smart observation here. She hasn't known Jeff very long, so she hasn't gotten accustomed to his quirks like his friends have. But, at the same time, she's listened to him complain about his boredom for long enough to know a few things about him. Like where his restlessness will lead: nowhere good.
STELLA: I can hear you now: "Get out of my life, you wonderful woman. You're too good for me."
Stella has got Jeff pegged. He's dissatisfied with a smart and gorgeous woman who would climb into a suspected killer's apartment for his sake. That unhappiness drives the romantic plot throughout the film; they're bickering when they should be falling into each other's arms.
JEFF: She belongs to that rarefied atmosphere of Park Avenue, you know. Expensive restaurants, literary cocktail parties. Can you imagine her tramping around the world with a camera bum who never has more than a week's salary in the bank? If she was only ordinary.
Here's a guy that can be unhappy about anything—even a smart, successful, gorgeous girlfriend who can't keep her hands off of him and wants to marry him. He assumes they're not compatible because of her glamorous lifestyle and hasn't given her a chance. She has to take matters into her own hands and prove him wrong.
JEFF: "Miss Lonelyhearts." Well, at least that's something you'll never have to worry about.
LISA: Oh? You can see my apartment from here, all the way up on 63rd Street?
Jeff assumes Lisa can have anything she wants, but she's no happier than he is. She wants to marry him but can't get him to commit and give up his travels. She's constantly being extremely seductive and amorous, but he ignores her. It's her unhappiness with the status of their relationship that pushes her to do something that might show Jeff that she can join him on his adventures: she climbs up a fire escape (in an elegant dress and heels) and sneaks into Thorwald's apartment.
STELLA: Poor soul. Ah well. Maybe one day she'll find her happiness.
JEFF: And some man will lose his.
Is marriage really that bad? Jeff is taking out his frustration about being confined to a wheelchair on poor Lisa, who's only trying to love him. This is one nasty comment about a woman who sure doesn't deserve it.
LISA: What makes you think something's wrong with [Thorwald's wife]?
JEFF: A lot of things. She's an invalid who needs constant care, and yet the husband nor anyone else has been in there all day.
Early in the film, Jeff sees Thorwald constantly being summoned by his wife, who's in bed sick. We get an idea why Thorwald is so unhappy in his marriage. Later, he's making long-distance calls and discussing his wife's jewelry—there's another woman, we assume. But as Lisa and Stella point out, lots of people are unhappy in their marriages but don't see it as a reason to dismember their spouses. Thorwald must be desperately miserable.
JEFF: Now, hold on. I'm not a bit squeamish about what might be under those flowers—but I don't care to watch two women end up like that dog.
Notice how powerless Jeff feels here: acknowledging that he wouldn't be able to do anything for Lisa and Stella if they should run into trouble. Nothing would be worse for this gung-ho guy than to sit by helplessly while the women are taking the initiative and at risk of getting hurt.