Aza tells Davis that she originally rubbed her thumbnail on her finger, giving herself a callus, to prove to herself that she was real. For her, it was like pinching herself to see if she was awake. The callus symbolizes Aza’s fears about not being “real” and her grief over the loss of her father. The callus is protective, like forming a layer over the wound of her heart.

Over time, the wound on her finger becomes part of Aza’s OCD ritual, as she tears open the callus, cleans the wound, and puts on a clean Band-Aid. This represents Aza’s need to exert control over her fears. She fears bacterial infection invading her body, which could grow beyond her power to stop it, resulting in her death. Each time Aza pushes her thumbnail into her callus, she is reestablishing her command over her existence. As the story progresses, Aza can’t relieve her anxiety by performing her ritual and adds the step of pouring hand sanitizer into the wound.

After Aza leaves the hospital, she allows the callus to heal, symbolizing her improved state of mind. As she experiences anxiety over telling Davis about his father’s probable death, however, Aza finds herself opening up the callus again.