In Part One, McMurphy's arrival begins to incite an attitude of rebellion in the patients, including Bromden, who have long accepted their place at the bottom of the hierarchy on the ward. Bromden lies in bed unmedicated for the first night in years, and he describes the sound of the ward with imagery that foreshadows major changes to come:
Not a sound across the hospital—except for a dull, padded rumbling somewhere deep in the guts of the building, a sound that I never noticed before—a lot like the sound you hear when you’re standing late at night on top of a big hydroelectric dam. Low, relentless, brute power.
It is possible that the boiler or other machinery in the building is really making a rumbling sound, and it is just as possible that Bromden is imagining the sound. Whether or not the sound is really there, what Bromden hears in the hospital is the sound of the hydroelectric dam that completely changed the ecosystem of his childhood home on the Columbia River. The dam symbolizes many things for Bromden. It stands for the way the United States has exerted destructive control over his people and their way of life. It symbolizes industrial development of many species' natural habitat. It symbolizes his father's turn to alcoholism and the grief that led to the end of his parents' marriage. And it symbolizes the societal forces that have traumatized him and led him to dissociate into hallucinations of fog.
What Bromden and the reader know in the back of their minds, however, is that dams break. They are built to harness the "low, relentless, brute power" of a river and convert it into electricity. The sound of the dam's power is also the sound of the river's power; that sound promises that one day, if the dam breaks, the river would come rushing forth again in full force. When Bromden hears the sound of a hydroelectric dam on the ward, he hears the sound of patients who are powering Nurse Ratched and who are simmering with their own "low, relentless, brute power," just waiting to break free.
In Part Four, during the nighttime party on the ward, Harding brings pills to Sefelt and Sandy after Sefelt has a seizure right next to her. He makes a speech that parodies a prayer on a battlefield and foreshadows a disastrous end to the party:
“Most merciful God, accept these two poor sinners into your arms. And keep the doors ajar for the coming of the rest of us, because you are witnessing the end, the absolute, irrevocable, fantastic end. [...] We shall be all of us shot at dawn. One hundred cc’s apiece. Miss Ratched shall line us all against the wall, where we’ll face the terrible maw of a muzzle-loading shotgun which she has loaded with Miltowns! Thorazines! Libriums! Stelazines! And with a wave of her sword, blooie! Tranquilize all of us completely out of existence.”
In Harding's speech, the "cc's" of drugs are bullets. The men on the ward are prisoners of war, and Nurse Ratched is the enemy executioner who is going to line them up against a wall and shoot them all. Harding prays to God to take mercy on Sefelt and Sandy and to welcome the rest of them to heaven when they, too, are medicated out of their minds.
Harding's speech is humorous, but it also helps Kesey emphasize that his novel is about more than mental health. Some of the men, including Bromden, are on the ward because of trauma they endured in World War II. The Vietnam War was underway when Kesey wrote this novel. Along with other members of the 1960s counterculture, Kesey felt that the war abroad was wreaking havoc on American men's psyches; he also felt that war was continuing to be waged on them at home by a society that was more committed to capitalism than anything else. By having Harding parody a battlefield prayer, Kesey brings the battlefield into the psychiatric ward.
The speech also foreshadows the events of the morning. Throughout the night, the men are optimistic that McMurphy will escape, and some of them will eventually follow. Harding's humorous speech is more in line with what actually happens. Nurse Ratched discovers the aftermath of the party and drives Billy into a shame spiral that leads to his suicide. She punishes McMurphy severely, eventually sending him for an ice-pick lobotomy that leaves him unresponsive to his surroundings. This one night of revelry really is the "absolute, irrevocable, fantastic end" of McMurphy's disruptive time on the ward.