Clarisse is full of life, questions, and curiosity. The value of life or "liveliness" in Montag's house is quite low. In fact, the liveliest thing in Montag's house is not Montag and Millie; it is the television shows on the parlor walls. The atmosphere in Montag's and Millie's house is cold, drab, and lifeless. Clarisse notes that she rarely watches the parlor walls; she'd rather spend her time outside, thinking, or talking. Clarisse notices things Montag and Millie don't even think about, such as the smell of old leaves. This is just one example which shows how Clarisse is interested in life while Montag and Millie are complacent with being sedated by their passive lifestyles. This idea of a sedated lifestyle has a literal correlation in that Millie takes sleeping pills and overdoses early in the novel.
The contrast between Montag's encounters with Clarisse and his life in his own house is shown early in the novel. After his first meeting with Clarisse, Montag reflects on the experience.
What incredible power of identification the girl had; she was like the eager watcher of a marionette show, anticipating each flicker of an eyelid, each gesture of the hand, each flick of a finger, the moment before it began.
A few sentences later, Montag's house is described as he opens the bedroom door to find Mildred passed out. This description immediately follows his lively encounter with Clarisse and presents the stark contrast between the two situations.
It was like coming into the cold marbled room of a mausoleum after the moon has set. Complete darkness, not a hint of the silver world outside, the windows tightly shut, the chamber a tomb-world where no sound from the great city could penetrate.
Note how Clarisse is described with attributes such as curiosity, awareness, thoughtfulness, and attention to detail. Montag's bedroom is described like a tomb.