What observations does Clarisse make about how Montag differs from other firemen?
In Fahrenheit 451, Clarisse appears very shocked to learn that Montag is a fireman. In her opinion, Montag is not like other firemen because he listens to the things she says. When she talks about the moon, for example, she notices that Montag looks up at it, as if he is really thinking about what she has said.
In addition, Montag enjoys his conversations with Clarisse which further differentiates him from other firemen:
"The others would walk off and leave me talking...You're one of the few who put up with me."
Clarisse also notes that Montag's friendly attitude towards her sets him apart from the others. She has clearly been bothered by firemen in the past, as she mentions that Montag does not "threaten" her.
In sum, Montag's friendly, relaxed and curious attitude is what sets him apart from the others. He and Clarisse are like kindred spirits: united by their interest in the world and their desire to look beyond mindless entertainment and censorship in their society.
Clarisse notices that Montag is a fireman right after she meets him, as she notices that he smells like kerosene. She tells him, "You know, I'm not afraid of you at all." Many people in their society fear firemen, who destroy books by burning them. However, Clarisse does not find Montag frightening and says that he just seems like a regular man. She is comfortable enough around Montag to ask him questions, such as whether he ever reads the books that he burns. She also asks him if he is aware that in the past, firemen extinguished fires instead of starting them. She watches Montag with her keen powers of observation and notes that he always laughs at things she did not intend to be funny and that he answers without thinking. She does not see Montag as a figure of brutal authority, the way other firemen are, and she likely senses that he will not turn her in to the authorities for asking incendiary—pun intended—questions.