Tobias's arm hurts from being shot, and he wonders about everything that exists outside the fence. There are greenhouses, and buildings, and lampposts, and weeds.
Tobias thinks about Evelyn, and about how she "pretended she could shape things from the wind" (12.9). But could she paint with all the colors of it?
The gang reaches the outer limit of the Dauntless patrols, and Johanna confesses that sometimes people would go outside the border. If that happened, they'd just reset their memories. Eternal Sunshine of the Dauntless Mind, if you will.
Tobias is in shock that memories can just be taken so easily.