At the opening of Samuel L. Clemens' "The Notorious Jumping Frog of Calaveras County," (also called "The Celebrated Jumping Frog of Calaveras County," the "notorious" probably developed as familiarity with the story's content grew and people realized how little the narrator was actually inclined to celebrate the story) the reader finds a first-person narrator who is comically cynical, a lovable curmudgeon who essentially tells the reader that what follows is useless information, and a waste of his time repeating it. Immediately he starts to throw out names and characteristics, of characters not yet introduced, and the reader will feel as though they've been dropped into the deep end of the pool.
There's a lot of logic to that since early versions of the story were printed in the form of a letter, and therefore it could be assumed safely that whoever the recipient of the letter was, might be "in on" something that we as readers are not.
Both the letter format and the setting--the American Southwest--were popular at the time. The prime example, up to that point, of the letter-writing style of story (called epistolary) was Bram Stoker's "Dracula." It's a form that's not used much anymore, but one of the things I found out when I was doing some research on the Internet is that it was the style used for Alice Walker's "The Color Purple" in the 1980s.
The story is really an update of an existing American "tall tale" about a grasshopper, and so it's possible that this was one of Twain's most "commercial" moves, specifically building a story that he knew would be well-received to anchor his collection of short stories. When he would travel around the country, this was a story that he passed on orally a lot, and eventually named...