In "The Most Dangerous Game," the plot moves quickly because of irony? Suspense? Characterization? or Details?
I would say that all of these aspects work in unison to help make Richard Connell's short story, "The Most Dangerous Game," a fast-paced, exciting tale. Certainly, the ironies of the situation--that big-game hunter Rainsford is himself hunted, and that the murderous Zaroff lives such an otherwise cultured life--help to maintain interest. The story is indeed suspenseful: The reader is left to wonder if Zaroff can really be serious about his human prey and if Rainsford can escape his own worthy adversary. The characters are drawn distinctly and in detail, showing both the positive and negative aspects and the strengths and weaknesses of both men. The setting and the subject matter are also highly interesting, and I personally enjoy the imaginative traps that Connell invents: The "Malay mancatcher," "Burmese tiger pit" and "native trick he had learned in Uganda" with the knife attached to a sapling are priceless. The title is well-named, with an obvious double-meaning; and, like all good short stories, "The Most Dangerous Game" has a surprise ending--or is it two?
In my opinion, the right answer to this question has to be suspense. This story certainly has a lot of suspense in it. In addition, I do not really think that those other things you mention can cause a plot to move quickly.
There is a lot of suspense in this story. For example, Rainsford falls out of the boat -- what will happen to him? He gets to Zaroff's home -- who is Zaroff? Zaroff explains the hunt -- what will Rainsford do? Once the hunt starts, what will happen? All of these questions make us want to hurry on and keep reading. I think they make use look forward and that makes the plot move quickly.