Sometimes, if I post on Twitter about a book I read and liked, I'll tag the author's account (if they have one). Once, the author replied back, a few times I've seen that they "liked" the Tweet. They get to see that someone liked their book, it's a bit of "word of mouth" for the work, and they're free to respond or not as they wish with no pressure.

I always took it as being a way to cover his own tracks (if an animal did it, he wouldn't be a suspect by default). Holmes himself points out that without tying him to the hound (which he had hidden really well and could theoretically put down and hide in the swamp if need be), there's no case against him beyond the flimsy circumstantial evidence.

While convoluted, the plan was more or less effective. The slip-ups that led Holmes to the truth were plausible ones that could be worked around (and the only one that really was his carelessness was telling Watson that he had been a teacher, since Holmes was able to use that background check him and figure out who he really was).