非言語コミュニケーション
Sherlock has a very unusual personality, and describes himself in the first episode "A Study in Pink", as a "high-functioning sociopath", a term he insists on in subsequent episodes. Others call him a "psychopath", and in "The Hounds of Baskerville" John Watson suggests to Lestrade that he believes Sherlock has Asperger syndrome. This manifests itself in very poor people skills and the extremely rude manners which Sherlock shows toward everyone he deals with. At times, he also seems to exhibit sensory sensitivities, associated with autism spectrum disorders, and occasionally exhibits "stimming" behaviors (pacing, hopping, spinning, rocking, making origami from serviettes, flapping a hand) when excited, upset, stressed, concentrating deeply, or overwhelmed. On two occasions in the episode The Hounds of Baskerville, he also appears to suffer from episodes of sensory overload and has minor meltdowns, and fidgeting with his hand after such an episode appears to soothe him. Also a characteristic of autism, Sherlock can be shown to have a very literal understanding of what is said to him – once, when after Sherlock tells John that he wants to go out that evening, John tells him that can't because he is going on a date, describing it as "two people who like each other [going] out and [having] fun", Sherlock replies that "That's what [he] was suggesting". Nonverbal communication also does not seem to come naturally to him, and he appears sometimes not to understand sarcasm, though he uses it often. During the episode "The Six Thatchers", John and Lestrade have a sarcastic conversation during which they compare Sherlock's neediness and selfishness to that of John's infant daughter, and although Sherlock is able to tell that they are making a joke about him, he does not fully comprehend. After asking them if they are making a joke, he admits that he "doesn't get it". He is also disdainful of the "typical" affectionate relationships he sees other people sharing, referring to them as "sentiment ... a chemical defect found on the losing side". He seems to admit that he does not understand sentiment and does not wish to, but he is shown throughout the series to care deeply about his closest friends. Sherlock is, however, skilled at feigning emotion and is shown successfully manipulating strangers – mostly by playing on their weaknesses – into helping him or providing information useful for a case. His brother Mycroft, in the first episode, says Sherlock has the mind of a scholar or philosopher.