What question by Clarisse makes Montag irritable? Why?

There are two questions really. One is if Montag knows there is dew in the morning. Montag is perplexed because he does not think about or notice such things. He doesn't like the thoughts his mind frets upon. Clarisse also asks Montag if he is happy. Montag doesn't know how to react. Montag doesn't know what happiness is. He has a sense that he is profoundly unhappy.