Why did Doyle choose Watson to narrate Hound instead of having Holmes tell the story himself? What are the benefits and drawbacks of doing it this way?
Doyle uses Watson as a narrator for two key reasons. In the first place, Watson is not as intuitive as Sherlock Holmes. In this sense, he allows the reader to join him as he attempts to live up to the master's standards. By contrast, if Sherlock Holmes were telling the story, we would have little opportunity to solve the mystery ourselves: witness, for example, Holmes' various and sundry revelations of the truth, which preclude our participation by effectively beating us to the punch.
The second reason Doyle uses Watson as a narrator is that it allows for the pace he is looking for. Even if Holmes' character can give us a chance now and then by keeping his conclusions to himself, he is still too quick a thinker to take on the onerous task of relating all the facts in detail. Only a slow-witted lackey like Watson is fit for the job. When Holmes' character does appear, he serves more as a catalyst for the action in the story, bringing things to a quick and exciting climax.
At the same time that Hound was written, Gothic fiction, which used supernatural themes, was extremely popular. Doyle himself was a spiritualist. How does the novel handle the possibility of supernatural occurrences?
The supernatural plays a major role in The Hound of the Baskervilles. Doyle uses it on multiple occasions in service of his plotline and in dialogue with other themes.
As far as plot goes, Doyle takes full advantage of the excitement, and power of a Gothic-style mystery-an ancient curse, and a common plotline, with two dead bodies at the hands of possibly a supernatural beast. At the same time, however, he evinces a strong faith, at least in Holmes, of a logical, rational explanation for even the most mysterious occurrences.
Thematically, the supernatural ties together questions of class, which run throughout the novel. Superstition is linked to weakness (as with the infirm Sir Charles), but most prominently with lower class status. In this sense, it is interesting that Doyle regularly refers to the superstitious commoners but only rarely lets us meet them first hand.
How do Sherlock Holmes and Arthur Conan Doyle handle class differences?
Both Holmes and Doyle come from a very specific and presumably similar cultural milieu in which gave privileges to the educated white male and denigrated virtually every other kind of human experience. Though they relied on and even fostered what might be called a space for only men, they almost certainly had no time for homosexuals. Though they relied on the lower classes to fetch them things and rummage through their garbage, they took little account of them or their dignity either. Two arguments can be made: one, that the prejudices of the past cannot be judged by the standards of our current cultural moment and two, that Holmes and Doyle were racist and sexist.
It probably makes the most sense to take the middle road, to situate classisms and racisms in their appropriate cultural context, while at the same time insisting on their inappropriateness in our modern world.