Vonnegut's humor is demonstrated primarily through the medium of black humor, a literary technique that makes us laugh so that we don't cry. Black humor is humor discovered in agony, despair, or horror. It can exist as an individualized hell or as a generally pessimistic view of the universe. In Slaughterhouse-Five, Vonnegut embellishes the scope of black humor by incorporating irony and by using vocabulary that creates a mock-serious tone, often leading to absurdity.
One example of Vonnegut's black humor concerns the British officers who welcome the American prisoners to the POW camp. These British officers, functioning in what would ordinarily be considered a demoralizing environment, manage to make the war experience seem less horrific than it really is. They treat the American POWs to a musical version of Cinderella during the first night in camp, an entertaining fare one would not typically expect in a German POW camp. With their incredible morale and elevated esprit, the British officers delight even the Germans who hold them captive. However, juxtaposed to this fantastical way of life is the fact that the Englishmen readily use objects of inhumanity without remorse. For example, their candles and soap, made from human fat rendered from Nazi war victims, are accepted without question. Slaughterhouse-Five is replete with such horrible compromise, yet the severity of these events is masked by Vonnegut's black humor.
On an individual level, the best examples of the novel's ironic black humor concern the hobo and Edgar Derby. The 40-old hobo, captured along with the American soldiers, continually assures his comrades that things "ain't so bad." He has been in boxcars before, he announces, but after nine days of confinement, he dies. Such situational irony is also evident in Derby's plight. He survives the bombing of Dresden, but he does not survive what follows. Having stolen a teapot, a minuscule item indeed, he is executed for the offense. For Vonnegut, the personal irony of the hobo's and Derby's situations magnifies the injustices of war, which often lead to the demise of individuals and their untimely deaths in absurd circumstances.
One additional technique that Vonnegut employs to set the tone of the novel's black humor is his use of words or phrases as a form of mock seriousness that gives way to the absurd. On the night of the Dresden bombing, Billy and his fellow POWs, as well as some of the guard detail, are underground in a meat locker that is used as a bomb shelter. Vonnegut's use of the term "meat locker" emphasizes that the prisoners are viewed not as humans by their captors, but as animals; after all, they are held in a slaughterhouse for animals. just as animals were previously killed in the Dresden slaughterhouse, so too, in theory, will many prisoners and civilians be killed — only the killers will not be Germans, but rather the American prisoners' fellow Allied soldiers. Other German guards, Vonnegut tells us, have "gone to the comforts of their own homes in Dresden. They were all being killed with their families." This tone of irony contrasts the human condition of life and family with the despair of death.
Another example of mock seriousness dissolving into absurdity is demonstrated in the dialogue of Wild Bob, the American infantry colonel who loses his entire regiment in battle. Waiting to be loaded into the boxcars destined for the POW camp, Wild Bob assures his men that there are dead Germans lying all over the battlefield who despair to God that they ever encountered the 405th Infantry Regiment, the regiment under Wild Bob's command. The seriousness of the situation quickly descends to absurdity as we realize that Wild Bob, critically injured and about to die, is losing his mind. The men to whom he speaks are not even part of his former regiment, yet Wild Bob hallucinates that they are. Even more pathetically absurd is his notion that the Germans died wishing they had never heard of his regiment: Wild Bob's soldiers, not the Germans, died on that battlefield.