How does the theme of obsession arise within the story about Kunicki?

The knife in this case is a symbol of domestic violence. Kunicki holds the knife as he cuts up parsley and once again interrogates his wife about her and their son's recent three-day absence. As he becomes angrier and more frustrated, he finally "throws the knife down into the parsley" and "the cutting board crashes to the floor" (336). The scene is a tense one and implies that Kunicki has within him the potential for violence.