There is of course one picture in this amazing book of a doorknob that appears in Oskar's notebook, we come to realise. When we think of the importance of keys and doors in the novel, the symbolic significance of this becomes very clear. It is particularly key (no pun intended) that the doorknob is something that opens a door, and symbolically allows the entrance and exit of certain aspects of our lives. This is a symbol that is replete with significance when we consider the way in which this novel is about one boy's search for closure of his grief and the way that his search has such an impact on those around him and the strange array of characters that he meets.
A central theme of the novel is dealing with death and loss, and we are presented with a number of characters who, for a variety of motives, have boxed in their grief and loss and who refuse or are unable to open the door to their grief. Gradually, through the novel, more and more characters are changed as a result of Oskar and his search to find what the key his father "left" him opens. If the picture of the doorknob and the closed door acts as a symbol it indicates the way that so many of us react to grief and loss through metaphorically closing it in in our lives. Oskar is the character who represents a force who opens that door and makes people's lives better as a result.