The Question and Answer section for The Curious Incident of the Dog in the Night-time is a great resource to ask questions, find answers, and discuss the novel.
Christopher finds a stack of his mother's letters to him in his father's room. This might be a clue to Wellington's death and more.
Christopher doesn't comprehend non-verbal responses like facial expressions because they're generally based upon human emotion (he also doesn't understand emotions). People also confuse him because they use different forms of language, and...
Yes Chris does find it difficult to answer the policeman's questions. The policeman is asking questions involving interpretation and emotion. Chris's brain has trouble processing these: he comprehends facts and concrete ideas.