Rue's Four Note Song

When Rue of District 11 worked high up in the trees, she used this song to tell her fellow harvesters when work time was over. She would sing the tune into the trees and the surrounding Mockingjays would pick up the song and sing it back to those on the ground.

The Hunger Games
During the 74th Hunger Games, Rue teams up with Katniss and whistles the song to let Katniss know she's okay. Katniss hears the song before she leaves to destroy the Career's camp but upon her return she hears Rue scream. When Katniss reaches Rue, tangled in a net, she sees a boy from District 1 putting a spear throuhgh Rue's abdomen. Katnissn kills the boy and rushes to Rue, who asks that Katniss sing her a song. Katniss obliges and, once Rue has passed, covers her in wildflowers. As she walks away, she sings Rue's little tune and has many dreams thereafter with Rue singing the song.

Catching Fire
During the victory tour an old man plays Rue's song to honor her. After the event he was killed along with many other people.

Trivia
At the end of every The Hunger Games trailer (with the exception of the first sneak peek), four whistled notes can be heard. These four notes, seemingly being Rue's four note song, are the same first four notes of the love theme from the 1968 film adaptation of Romeo & Juliet. Interestingly enough, the song, entitled What Is A Youth?, starts with that very question and those same four whistled notes might be posing that question to The Capitol.