The planet of Tralfamadore, where Billy Pilgrim and Montana Wildhack are held in a zoo, can be read as a symbol for the worldview that allowed Billy to assimilate his war experiences into his post-war life. The Tralfamadorian view is that time is an established series of events devoid of morality and cause and effect relationships. Further, while bad things happen it is best to focus on the good times. The zoo is a suspended reality, in which Billy lives out his dreams (like coupling with a starlet) and receives lessons about the nature of the universe. The dwelling in the zoo, furnished with catalog furniture and a television with a picture of one cowboy killing another, symbolizes the middle-class trappings of Billy's post-war life. He is a success by the standards of his peers yet he feels as satisfied in his home as he does on an alien planet. In this manner the dwelling on Tralfamadore provides Billy with the perspective he needs to judge his life and the flexibility to adopt a new outlook.
The Barbershop Quartet
The group of four optometrists who sing sentimental songs figures prominently in two portions of the novel and in each case they are harbingers of doom. The first time they are presented is on the fatal plane ride that ends when the aircraft hits Sugarbush Mountain. In this case, the group's bawdy songs and light-hearted ditties serve as a reminder that horrible events occur in the context of hilarity and pleasure. The second time we meet them is years before the plane crash at Billy and Valencia's anniversary party. On this occasion the sight of the quartet causes Billy to suffer tremendous mental anxiety. Upon reflection he realizes that the quartet has reminded him of the almost comical appearance of the four German guards the morning after the attack on Dresden. In this manner the barbershop quartet, as represented by the German guards, again symbolizes the juxtaposition of horror and hilarity.
Dresden, described as the most beautiful city many of the POWs had ever seen and appearing to look like the mythical Oz, symbolizes the innocence and purity of peaceful, happy living. As such, the senseless destruction of the city and its inhabitants symbolizes the inexplicable and often traumatic permutations of modern life. The day following the firebombing Billy and the other survivors simply go on dealing with the details of living and it is not until many years after the war that the trauma of the event begins to assert itself. Once Billy has assimilated the war into his Tralfamadorian philosophy, however, he is able to view Dresden's destruction as an unavoidable event that carries no particular meaning. This is why he is able to agree with the military apologist Rumfoord that the men who ordered the attack were not evil but simply doing their job.
Kurt Vonnegut has said that the character of Kilgore Trout, who appears in many of Vonnegut's novels, represents what he might have become if his writing career had not met with success. Within the context of Slaughterhouse Five Trout and his stories symbolize the real world (which is to say, Earth bound) ramifications of the Tralfamadorian philosophy. As such, when Trout reinvents the story of Jesus to produce a more universal moral it resonates with Billy's efforts to assimilate his war experiences into the greater scope of time.
Writers who are trying to convey the horror of way often use animals to convey the true sadness and terror of the experience. This is true of writers like Erich Maria Remarque (All Quiet on the Western Front) and Tim O'Brien (The Things They Carried) and it is true of Kurt Vonnegut as well. Following Billy's pleasant nap in the back of the wagon, two German obstetricians are horrified at the miserable condition of the horses and confront Billy who had not noticed that the animals were suffering. At this moment, Billy bursts into tears his only emotional outpouring in the course of the novel. In this way, the horses symbolize the needless suffering brought about by the war and the manner in which that suffering goes largely unnoticed by those caught up in the events. Moreover, they represent the latent pain present in all those who witness horrific events.