The very first time that Montag meets Clarisse, she mentions how people are so rushed these days that they don't even notice the little things. She says, "I sometimes think drivers don't know what grass is, or flowers, because they never see them slowly...if you showed a driver a green blur, Oh yes! he'd say, that's grass! A pink blur! That's a rose garden. White blurs are houses. Brown blurs are cows." She even talks about the 200-foot long billboards, there because "cars started rushing by so quickly they had to stretch the advertising out". Later, the last time that Montag sees her, she says that for fun, kids her age "go out in the cars and race in the streets, trying to see how close you can get to lampposts, playing 'chicken' and 'knock hubcaps."
Both of these quotes emphasize the need for thrill, entertainment, and speed in their society, which they use as a violent sort of catharsis, drowning all thought and sorrow. I hope that one of those quotes was the one you were looking for. Good luck!
In the exposition of the narrative of Fahrenheit 451, author Ray Bradbury introduces characters as well as details of the setting. The character Clarisse McLellan, a pedestrian in a world where no one walks, is more like the people of the time of the novel's publishing (1950's). Because she walks around her neighborhood, Clarisse takes notice of the behaviors of the residents there and in nearby areas.
After work one night, Montag encounters her on a corner, and she inquires if it is all right if she walks with him on the "silvered sidewalk" while she answers his questions. Clarisse tells Montag that she enjoys smelling things and looking at things. Sometimes, she adds, she stays up all night until the sunrise. But, when she questions Montag, he responds spontaneously, causing Clarisse to remark,
"You laugh when I haven't been funny and you answer right off. You never stop to think what I've asked you." (p.6)
Then, Clarisse asks Montag if he has ever watched the jet cars racing on the boulevards down the way. She notes,
"I sometimes think drivers don't know what grass is, or flowers, because they never see them slowly...if you showed a driver a green blur, Oh yes! he'd say, that's grass! A pink blur! That's a rose garden. White blurs are houses. Brown blurs are cows." (p.6)
Here Clarisse's observations point to how mindlessly people exist. They do not stop to think about anything, or to enjoy what they can see. Clarisse tells Montag that her uncle once drove forty miles an hour, and he was jailed for thirty days. When he hears this, for some reason Montag responds with unease: "You think too many things." As explanation, Clarisse says that she rarely watches the 'parlor walls' as do others—nor does she go to the races or Fun Parks. "So I've lots of time for crazy thoughts, I guess," Clarisse remarks.
It is interesting that Clarisse considers her thoughts "crazy," when, in reality, the others in this new society go about mindlessly. Montag's is intrigued by his encounter with this unique young woman, who alludes to activities in which Montage's wife Mildred engages.