The mood shifts according to the point-of-view in "An Occurrence at Owl Bridge" by Ambrose Bierce.
As the story opens the mood is stoic; the scene portrayed reads more like a report of how the soldiers operate. Bierce provides minimal details of any emotion to the reader in the opening paragraphs, except to comment on the absence of it, such as: "The company faced the bridge, staring stonily, motionless" (1). This first section of the story reads like an indifferent soldier's report.
The mood shifts as the point-of-view changes to that of the young man. At this point in the story, the mood becomes increasingly tense and distracted, because the young man in question faces the hangman's noose and contemplates his final moments. Perhaps because Fahrquhar knows that he is about to die, he lets himself be distracted by his surroundings:
The water, touched to gold by the early sun, the brooding mists under the banks at some distance down the stream, the fort, the soldiers, the piece of drift -- all had distracted him. And now he became conscious of a new disturbance. (2)
Finally, as Fahrquhar begins his downward plummet, the mood shifts to desperate as he plunges into the river below to try and free himself:
"Put it back, put it back!" He thought he shouted these words to his hands, for the undoing of the noose had been succeeded by the direst pang that he had yet experienced" (4).
Bierce increases the intensity of the moment by using shorter sentences to create an infusion of sensory details like "his neck ached horribly, his brain was on fire" (4). The reader experiences the sense of panic right along with the character.
One of the most interesting aspects about the shifting moods in this story is that Ambrose Bierce frequently interjects beautiful, descriptive imagery and sentences in between the sequences of terror felt by Peyton Fahrquhar. For example when the young man imagines his home "all bright and beautiful in the morning sunshine," the lovely imagery helps to take the edge or cold-heartedness of the man's hanging (7). The connection to nature softens the mood from being overly harsh.