In Fahrenheit 451, Clarisse is different than most of her peers because of her unique way of thinking.
Clarisse differentiates herself from other people because of the distinctive way she looks at the world. She reveals this in her conversations with Montag. For example, Clarisse talks to Montag about things he has never considered. She talks about the taste of rain and how there is someone on the moon. In these instances, Clarisse defies social expectations. She is willing to think and act very differently than conventional behavior.
Clarisse identifies herself as different because of her willingness to think and articulate her thoughts. She enables Montag to realize there might be something deeper in the world:
"You're one of the few who put up with me. That's why I think it's so strange you're a fireman, it just doesn't seem right for you, somehow.'
He felt his body divide itself into a hotness and a coldness, a softness and a hardness, a trembling and a not trembling, the two halves grinding one upon the other.
Clarisse sees herself as fundamentally different than the rest of the world. When she tells Montag that he is "one of the few" who can tolerate her, Clarisse acknowledges her uniqueness. She is not like her peers. She is unlike anyone Montag has met. Her willingness to see what others might miss makes her different. Clarisse's distinct condition helps Montag realize the world might not be what it appears to be. When Bradbury describes Montag's body as dividing itself, it is clear Clarisse's distinctive nature has begun to affect him.