How is Christopher an unreliable narrator in Curious Incident of the Dog in the Night-Time?
Christopher is to some degree an unreliable narrator because, as a person on the autism spectrum, he finds human emotion and motivation confusing. For example, he thinks that his father is going to kill him because his father killed the neighbor's dog. The reader, on the other hand, knows that Christopher's father, while feeling overwhelmed by raising a boy with autism, is a loving father who is committed to raising his son and who is not murderous.
On the other hand, in some ways, Christopher is very reliable. He is flawless when it comes to observing material facts. He is very logical in certain ways and is committed to figuring out who killed the neighbor's dog. He notes that he first sees the dead dog at seven minutes after midnight and that the dog must have died when someone stuck a garden fork in it because there were no other wounds, and a person was unlikely to have stuck a fork in the dog after it had died in some other way. He is adept at observing material facts, such as the number of holes in one's shoes, and, in this sense, he is a reliable narrator.
Christopher's worldview is limited in scope in part because of his neurodiversity, but also because of his lack of maturity and exposure to life experiences. Because of his youth, self-selected interest areas, and his parents' choices, Christopher has had little opportunity to acquire wisdom and perspective about the world around him. His narration demonstrates a lack of understanding of the nuance and sophistication of the emotions and motivations of the adults he interacts with over the course of the story. It reflects his inability to comprehend of the complexity of his universe.
Christopher's motivations are simple, straightforward, and based primarily on his personal logic, i.e. my father killed a dog, therefore he is dangerous to me. His narration reflects these conclusions and limits his perspective of the events that unfold as pertaining solely to the motivations that resonate within his own sphere of understanding: namely survival, following rules, and problem-solving.
I can address the idea of Christopher as an unreliable narrator. There are many instances in the novel when the reader can piece together more of the situation than Christopher himself. For example, a careful reader can figure out Christopher's mother has been having an affair with the neighbor's husband without Christopher having to mention the fact--or even realize it. His voice as an unreliable narrator adds humor to tense situations (like in the opening scene where he punches the police officer) and offers a unique perspective throughout the story. The title itself seems like one that Christopher would pick out. Not many people would describe a deadly attack on a dog as "curious"--it seems far too understated. Unreliable narrators may be limited to their own skewed perspective of reality but careful readers can usually re-create what is actually going on by piecing together subtle details the narrator himself may not understand.
Christopher is an unreliable narrator, in part, because he has an autism spectrum disorder. People on the spectrum often perceive the world around them differently from people who are not on the spectrum because they can have difficulty reading social cues and sorting through sensory information. Christopher's difficulty in reading social cues is likely why he does not realize that his mother is having an affair despite the fact that it is obvious to us. In addition, his response to death of the dog named Wellington is curiosity as opposed to horror or shock, which makes him seem guilty to people who do not understand the way his mind works. Christopher's processing difference might affect the kinds of information he shares as well as the way he shares it.