Sherlock Holmes on Dogs

From “The Creeping Man”:

“You will excuse a certain abstraction of mind, my dear Watson,” said he. “Some curious facts have been submitted to me within the last twenty-four hours, and they in turn have given rise to some speculations of a more general character. I have serious thoughts of writing a small monograph upon the uses of dogs in the work of the detective.”

“But surely, Holmes, this has been explored,” said I. “Bloodhounds—sleuth-hounds—”

“No, no, Watson, that side of the matter is, of course, obvious. But there is another which is far more subtle. You may recollect that in the case which you, in your sensational way, coupled with the Copper Beeches, I was able, by watching the mind of the child, to form a deduction as to the criminal habits of the very smug and respectable father.”

“Yes, I remember it well.”

“My line of thoughts about dogs is analogous. A dog reflects the family life. Whoever saw a frisky dog in a gloomy family, or a sad dog in a happy one? Snarling people have snarling dogs, dangerous people have dangerous ones. And their passing moods may reflect the passing moods of others.”