Cutters
The group of Cutters is symbolic because of the way they came about and the reasons that they cut themselves. They first became a group when, as pretties, they wanted to feel something, to clear their minds or become "bubbly". Zane is the one who starts to question Tally, his questioning being the starting-point of her change.
"What is it that you're not feeling, that you have to do that?-Zane asking Tally about her cutting.
Andrew Simpson Smith
We meet Andrew Simpson, the village priest from the previous novel, once again. This time he managed to escape the experimental wilderness and is now on the mission to help runaways reach The New Smoke. Andrew Simpson Smith is a representation of a man that trusts his instincts, a man who spent his whole life in nature and Tally feels herself unable to lie to him, even with her artificially designed body and sharpened senses. He makes her question herself, what she's turned into and steers her into change.
Civilization of Rusties
Civilization of Rusties represents a reminder, a motif, of the destruction that humanity is capable of. They recklessly destroyed nature and destroyed themselves eventually. At the end, Tally warns the others, The New Smoke to be careful not to follow in the Rusties' footsteps.
Hunger for power
Dr. Cable used Tally's and Shay's break into the Armory, to her advantage. She is cruel and hungry for power and at one point takes over the entire city, which seems to have been her plan all along. In the novel, Tally injects Dr. Cable with the cure and she turns good and heroic at the end; the existence of such a magic pill or injection in the real world might be useful as well.
