"I adjusted the string so the keys—one to the apartment, one to I-didn’t-know-what—rested against my heart, which was nice, except the only thing was that it felt too cold sometimes, so I put a Band-Aid on that part of my chest, and the keys rested on that."

Oskar says this in Chapter 9, when describing how his quest for the lock and the key itself become the only things that make him happy. Throughout the novel, keys act as a symbol for the ways people become closer, and Oskar always states that he believes the mysterious key will allow him to unlock something about his father. By holding the key over his heart, he therefore keeps his dad close. Oskar’s quest for the lock evokes the last Reconnaissance Expedition his dad sends him on, in which his dad tries to teach him how to find joy in the search. The very act of searching through New York City allows Oskar to follow his dad’s example in how to approach unsolvable problems. In addition, Oskar has previously observed that his dad’s ashes have become a part of New York City. As his quest takes him all over New York, he literally becomes closer to his dad by exploring all the places his ashes have gone. 

This quotation also foreshadows a possible resolution to Oskar’s grief. Oskar views the key as bringing him closer to his dad. By keeping this key over his heart, Oskar keeps the memory of his dad close. However, just like the key gets cold, so does this memory sometimes hurt. We can read the Band-Aid, which acts as an intermediary between cold metal and skin, as representative of a way to keep his dad’s memory close without feeling the full force of that grief. For Oskar’s mom, holding a funeral even though they didn’t have a body allows her to adapt to the reality of his death without drowning in grief. It doesn’t erase the pain or her memories of Oskar’s dad, but it dulls the sheer harshness of the truth. At the end, Oskar’s rewinding time and reliving his last moments with his dad serves a similar role. Up until then, Oskar focused solely on the moment of his dad’s death and the questions it raised. By reliving his dad’s story time, Oskar can relive a moment of security where he felt loved, a Band-Aid to help him heal from his grief.