Though this question asks for two observations, more than two are actually observable during the initial interaction between Clarisse and Montag.
Within the first moments of their meeting, Clarisse tells Montag that she does not feel scared of him at all, despite his role as a fireman. This feedback suggests that Clarisse finds Montag's conversational style and his mannerisms unexpectedly approachable.
Later in the conversation, when Clarisse asks Montag questions about his work, he laughs at her, and she says to him, "You laugh when I haven't been funny and you answer right off. You never stop to think what I've asked you." She observes that he laughs at what she perceives to be odd or inappropriate moments and that he does not take much time to consider her questions; both of these observations take Montag by surprise, and he feels the need to prove himself by showing Clarisse the 451 numerals on his uniform.
Finally, Clarisse asks Montag if he is happy as she goes into her house. This...
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