Holden's 10-year-old sister, Phoebe, is bright, pretty, mature beyond her years, sane, and his most trusted link to family. She has red hair and is "roller-skate skinny," a metaphor that, Salinger seems to be saying, is like jazz; you either understand it when you hear it, or you never will. Phoebe's favorite movie is the Hitchcock film The 39 Steps (1935); she has committed the dialogue to memory. She is successful in school, her best course being spelling. She is the one who corrects Holden concerning the words to the Robert Burns poem that is the source of the novel's title. In her spare time, she writes fiction featuring a girl detective, an orphan named Hazle Weatherfield. Phoebe later adopts "Weatherfield" as her own middle name. She likes elephants and has red ones on her blue pajamas. She studies belching with a friend named Phyllis; her best friend, Alice, is teaching Phoebe to induce a fever artificially by crossing her legs, holding her breath, and thinking of something very hot. She conscientiously promises not to burn Holden while demonstrating her trick.
Holden's adolescence and his confusion complicate the relationship with Phoebe. While she sometimes seems to be his best friend, at other times he is acutely aware of her sexuality or need for independence. Twice (Chapters 10 and 21) he says that she can sometimes be too affectionate. Although he is capable of giving her "a pinch on the behind," which is "sticking way out in the breeze," he knows better than to put his hand on her shoulder at the wrong time. When Phoebe rides the carrousel, Holden realizes that there are times when kids want to try to grab the gold ring, symbolically taking a chance in life, and he must allow her the freedom to do that, even though she may fall. That realization is a big step for Holden. All things considered, the relationship between Holden and Phoebe seems healthy and normal for caring siblings. It is in flux, as is everything in life, and Holden may regret that. But he shows he has grown when he realizes that Phoebe can't stay 10 years old forever.
For her part, Phoebe sometimes sees right through her brother. She realizes early in his visit that he has been expelled from Pencey. On the other hand, some of Holden's darker thoughts are beyond her. She can't fathom why he is so self-destructive or why he doesn't just succeed in school the way she does. When he bares his soul to tell her of his dream of being "the catcher in the rye," she is quiet for a long time but then simply states, in reference to his expulsion, "Daddy's going to kill you," illustrating that despite their great friendship and connection, Phoebe is still only 10 years old and cannot be expected to understand the true meaning of Holden's words.