An old pipe runs from the stream at the brush line into an old tub. Around this tub the grass is perpetually green, and Jody often goes their for comfort. The moral opposite of the green patch is the cypress tree and the black kettle used to slaughter pigs that sits under it. After talking to Billy about the possible dangers of Nellie's birthing, Jody walks to the house in a worried state. Suddenly he finds himself under the cypress tree. He takes this as a particularly bad omen.
Jody walks over to the green patch, imagining now that Nellie will produce a fierce black stallion. He fantasizes about being a hero, helping out the sheriff, winning rodeos, all because of his horse, which in his revelry he dubs Black Demon.
The year passes slowly. One day, Jody's mother prepares a warm mash for Nellie, and Jody finds that the horse has swelled considerably. Winter comes fast, and the colt is due in mid-January. Jody is alarmed at how big Nellie has grown, and childishly asks Billy whether Nellie will just burst open. Also, Carl Tiflin complements Jody on how well he had done with Nellie, and Jody beams with pride for a day, since compliments from his father are so rare.
As January passes, Jody grows frantic that the horse is late giving birth. One night, he goes to the barn in a sweat, worried that something has happened. Billy, who is asleep in the barn, growls at Jody to go back to bed. Jody creeps back into the house. His father wakes up and, fighting anger, tells Jody not to worry. When Jody blurts out that Billy let Gabilan died, his father sternly tells him not to blame that on Billy.
That morning Billy wakes Jody, telling him to hurry to the barn. Nellie is having spasms. Billy mutters that something is wrong, and swears. He feels the belly of the horse, and makes a careful diagnosis with his hands. He gives Jody a long, interrogating look, then reaches for a hammer and asks for Jody to leave. But Jody doesn't move. Billy is gray and drawn. He brings the hammer down on Nellie's forehead twice, she falls, and he immediately begins sawing at her stomach with his pocketknife. The barn fills with the smell of entrails, and the other horses in the barn squeal and kick. Billy lays the little black colt he has dug out at Jody's feet. It draws a gurgling breath. Billy says there is the colt, as he promised. Jody aches on the inside.
This story is in many ways the climax of the novel. A continuing theme throughout The Red Pony is the somewhat dysfunctional relationship between Jody and his father, and the way Billy sometimes is a more ideal father to Jody. In The Promise, we see Billy's frustration with having failed Jody by letting Gabilan die come to a head. By the time Billy has to kill Nellie in order to produce the colt he has promised Jody, he seems to resent the moral burden placed upon him to please Jody.
Although the colt is born, it is at a great cost. This is foreshadowed by Billy's early discussion of the possible difficulties of birthings, by Jody's pessimistic thoughts under the cypress tree, and even by the gory details of the story of Gabilan. Jody continually sees the raising of horses as an ideal. Even after Gabilan dies, he is able to fantasize about his new horse making him a hero. But his relationship with horses never works out seamlessly, signaling that nothing is ideal in the harsh reality of the West. When his new horse is birthed out of the death of its mother, Jody must face the crumbling of the illusions; he has exactly what he wants, a healthy, strong horse, but it came at a price that Jody cannot and, as is evident in his refusal to leave the barn, will not ignore. In gaining a horse at the cost of its mother, Jody must face the ridiculousness of his fantasies about "Black Demon." Once again, Jody's romanticized notions of the world he lives in have been punctured.