"You have heard me speak of Professor Moriarty?"
"The famous scientific criminal, as famous among crooks as --"
"My blushes, Watson," Holmes muttered in a deprecating tone.
"I was about to say, as he is unknown to the public."
-- The Valley of Fear, Chapter 1
This dialogue from the opening chapter of the last canonical Holmes novel looms large in my memory as a priceless piece of wordplay between Holmes and Watson. But not because of the novel itself.
I have thought about it often for more than forty years now mostly because Christopher Morley called it my attention. He begins his classic essay, "In Memoriam Sherlock Holmes," the introduction to the Doubleday Complete Sherlock Holmes that so many of us know so well, by observing: "It was unfair of Conan Doyle to say (as he did in his delightful autobiography Memories and Adventures) that Dr. Watson had never shown a gleam of humor nor made a single joke."
He then cites the passage above as an example of a Watsonian joke. The passage is also perhaps the only time that Watson "caught Holmes fairly off guard," as Morley put it.
Of all the dozens of introductions I have read to collections of Sherlock Holmes stories, Morley's remains my favorite -- although Howard Haycraft and Loren D. Estleman wrote great ones, too.
What is your favorite introduction to Sherlock Holmes? Please tell me -- I really want to know!