Branches as bone, paper as heart and skin
We have the following quote in Chapter 5: “These branches will be my bones, I thought, and the paper will be my heart and skin, the places that feel everything” (p. 58). This is a great example of imagery in the form of the things that Cassia holds on to while she's away from Ky working in Central. The naturalness of the branches and familiar forbiddance of the papers provide a second body of sorts to hold her together until she can see him again.
Fragile skin and haunted eyes
When Cassia initially sees the still hooked to IV drips on her port, she thinks to herself, "Is this a new plan of the Society's? First they take our memories, then they drain our blood, until we are only fragile skin and haunted eyes, shells of who we used to be" (page 91)? This is a gruesome image displaying her fear of the worst the Society could do, though ultimately a bit of an inaccurate one.
A hook of moon
Ever the poet, Cassia describes the night on p. 55 by saying, "I see a hook of moon tipped in the dark blue water of the evening sky." This conjures up an excellent mental image of the moon floating in the sky as if it were made of water.
Dead fish in the lake
On p. 68, we get a disturbing mental image when Cassia describes "dead fish [lapping] along the bank... Belly-up, glazed-eyed." She likens this experience to Ky finding Vick's dead body by the poisoned river, an even more horrifying comparison that creates a dark, even creepy mood.