Some stories go along just fine, with integers as chapter numbers. One, Two, Three, etc. Some even use real numbers, Chapter 1, Chapter 2, etc. Why do some authors use chapter names like Chapter 3A or 2.5? Have they had a sudden inspiration and want to fit new information into the story in a "chapter" that goes between other chapters with whole numbers? Or did they drop chapter 3 and substitute an alternate, Chapter 3A?
On an almost unrelated topic (thread drift while the thread is new), there are some authors that kinda/sorta describe what the chapter is about. Like "Chapter 27, Off to University." Or "Chapter 69, Mutual Oral Sex." Why do they decide to do that and how do they think of the descriptions? Is it foreshadowing or just giving away the plot of the chapter?
One of the benefits of being an author is getting to make those decisions, I don't want to take any of their super-powers away with reviewer kryptonite, but are there explanations mere readers can learn to improve the awe we feel in the presence of greatness?