How we cite our quotes:
As I drifted, I dreamed. […]
Where I floated, under the dark water, I heard the happiest sound my mind could conjure up – as beautiful, as uplifting, as it was ghastly. It was another snarl; a deeper, wilder roar that rang with fury. […]
And then I knew I was dead. (23.1, 2, 4)
Bella is recovering from being attacked by James, but she believes she's dead. It seems that she thinks the most beautiful sound she can imagine is Edward's snarl as he comes to defend her. Why is it that Bella knows she is dead? What convinces her?
[Edward as heard by Bella:] "Carlisle!" the angel called, agony in his perfect voice. "Bella, Bella, no, oh please, no, no!" And the angel was sobbing tearless, broken sobs. (23.11)
Bella thinks she has died and that Edward is an angel.
[Bella:] "You're wrong," I insisted. "I'm going to die. […] I may not die now…but I'm going to die sometime. Every minute of the day, I get closer. And I'm going to get old." (24.223, 225)
Bella reminds Edward of a central conflict in their relationship: she will grow old and die, while he is immortal. She wants him to transform her into a vampire so they can share eternal youth.