But I came to believe that if I watched closely, and desired, I might change the lives of those I loved on Earth. (2.39)
Much of Susie's earthly interactions are fairly subtle. She does lots of showing herself to people in glass, and she blows out a candle and maybe drops an icicle here and there. When she goes into Ruth's body and makes love with Ray, she's taking it to the next level.
"I was crossing through the faculty parking lot, and suddenly, down, out of the soccer field, I saw a pale ghost running toward me." (3.5)
When Ruth tells her mom this, she isn't sure she wasn't dreaming. But, she soon faces the fact that Susie did indeed touch her on the way out. And when you're touched by a ghost, you better take it seriously.
It was then that, without knowing how, I revealed myself. In every piece of glass, in every shard and sliver, I cast my face. (3.64)
After smashing up the ships in bottles, Jack gets to see Susie's face. It's then that he figures out that Mr. Harvey is her killer.
Had my brother really seen me somehow, or was he merely a boy telling beautiful lies? (7.35)
Susie has been trying not to think of Buckley too hard. When she thinks of people too hard, they might see her in the glass. There's a fine line between memory and imagination, and really seeing a ghost.
I listened to the sounds and felt the train's movements and sometimes, by doing this, I could hear the voices of those who no longer lived on Earth. Voices of others like me, the watchers. (17.104)
In this novel, the dead fill the world of the living. But they are restricted to the role of passive "watchers" that aren't involved in the living world (or not much, at least).
I had told people about her, what she did, how she observed moments of silence up and down the city and wrote small individual prayers in her journal, and the story had travelled so quickly that women lined up to know if she found where they'd been killed. (18.10)
"Someone came in the room and then left. I think it was Susie." (20.81)
Jack always embraces ghost Susie. He sees her like she sees herself – as someone who lives somewhere else, but can still come back and visit. Abigail has a much more guarded attitude toward the whole ghost thing.
That was the moment I fell to Earth. (21.161)
Susie puts the "super" in supernatural. Here she's at the height of her realm switching powers.
On that same road where I had been buried, Mr. Harvey passed by Ruth. All she could see were the women. Then: blackout. (21.160)
Ruth's supernatural ability is just too much for her.
"I've watched you both for years," I said. "I want you to make love to me." (22.125)
Susie is no cheesy succubus using humans for sex against their wills. No, Ray will only make love to Ruth's body when he learns Susie's inside it. It's consensual, and it seems to be a positive experience for him. For Susie, it's a chance to move past her brutal experience with Mr. Harvey and have a loving sexual experience. We get the feeling that now she can move on.
"We're here, you know […]. All the time. You can talk to us and think about us. It doesn't have to be sad or scary." (22.154)
Susie is saying that what we've been talking about as supernatural interactions between the living and the dead are really quite natural. What do you think?