In part 1, section 16 of Fahrenheit 451, when Millie can't answer the question, what does she get up to do?
Montag is still thinking about all that has happened since the beginning of the story. Clarisse's question to him about whether or not he is happy, her suggestion that he might not be in love, the death of the old woman who would not give up her books are all events that are weighing heavily upon Montag. He asks Millie if she can remember when and how they met ten years earlier because he cannot. She doesn't remember either. Montag realizes how shallow their existence is; how devoid of real emotion or love. After Montag asks Millie the question, she gets up, goes to the bathroom and Montag can hear her pouring a glass of water and then swallowing. He tries to count the number of swallows and wonders how many of those pills she had taken already that night. He knows that if she died from an overdose, he would not cry because he doesn't really have a connection to her. He is very saddened by the emptiness. Millie's actions reveal that she, too, is not happy. She takes the pills to avoid reality. Reality is cold and sterile in their world and that hurts, so Millie hides behind the chemical relief of the pills. She is like most of the people in that society - escaping a harsh, cold reality for a less painful chemical addiction.