Roark's words were like the steps of a man walking a tightwire, slow, strained, groping for the only right spot, quivering over an abyss, but precise. (1.8.23)
Rand uses a metaphor of a tightrope walker to describe Roark's tense manner of speaking. She also compares misspeaking to falling into "an abyss": you better believe that Ayn Rand was a firm believer in saying the exact right thing.
Then the thing which happened hit Peter on the back of the head; it was not a sound or a blow, it was something that ripped time apart, that cut the moment from the normal one preceding it. (1.9.52)
The rather lengthy descriptions of Toohey speaking at a rally are kind of terrifying. Toohey here comes across as a force of nature capable of ripping time apart, like a philosophical atomic bomb.
"I think it would have been better if you hadn't told me that you liked me. Then I would have had a better chance of its being true." (1.10.97)
Here Dominique proves herself to be a certified cynic: according to Dominique the best way to be assured that someone doesn't like you is for them to tell you that they do like you.
He knew while he spoke that it was useless, because his words sounded as if they were hitting a vacuum. (1.13.76)
Language can be something very powerful, but only if you're speaking to a receptive audience. Otherwise, you might as well stay silent.
"You'll be exposed publicly," said Keating, the sounds of his voice glittering. "You'll be denounced as a grafter." (1.15.30)
Keating's voice is clearly bedazzled. When Keating is in his heyday, everything he does is evocative of wealth: even his voice is diamond-studded.
"He said, Wait a minute, and he read it again, he looked up, very puzzled, but not angry at all, and he said, if you read it one way [...] but on the other hand [....]" (2.8.145)
Roark relates an incident of someone reading Dominique's column and hitting upon the double meaning behind her words. Most characters in this book are pretty straightforward, but Dominique in embraces the nuances of language.
"I want to ask every man who is interested in this to go and see the building, to look at it and then to use the words of his own mind, if he cares to speak." (2.12.45)
Roark encourages people to form their own opinions and speak their own minds here. Everything for Roark ties back to his strong individualist views.
They could always speak like this too each other, continuing a conversation they had not begun. (2.12.63)
This quiet sense of connection between Roark and Dominique is a recurring motif throughout the latter part of the novel.
Queer things were happening to Keating's verbal punctuation: some words came out crisply, as if he dropped an exclamation point after each; others ran together as if he would not stop to let himself hear them. (2.12.133)
Rand often describes how people speak rather than just telling us verbatim what they are saying. Here, we don't really need to know what Keating is saying about Roark in his testimony. We get a lot more insight into Keating's state of mind by learning about how he sounds.
"You wanted an act to help your act—a beautiful, complicated act, all twists, trimmings and words. All words." (3.2.142)
Dominique basically calls Keating out as being a performer, or a showman. Why? Because Keating's words aren't backed with actions. He talks the talk, but he does not walk the walk.
He settled back, to enjoy a long speech of persuasion. He thought it would be interesting to hear what arguments she'd choose and how she'd act in the role of petitioner. (3.3.103)
Toohey loves messing with people, and he also enjoys playing with language. His love of language is kind of endearing… or it would be if he weren't so freaking evil.