The guards standing watch over the Americans sheltering in the slaughterhouse during the bombing of Dresden are compared to a barbershop quartet with a simile:
The guards drew together instinctively, rolled their eyes. They experimented with one expression and then another, said nothing, though their mouths were often open. They looked like a silent film of a barbershop quartet.
The optometrist barbershop quartet is mentioned frequently throughout Slaughterhouse-Five, and often triggers memories of wartime. The above simile, comparing the guards to a barbershop quartet which was not singing, explains why that might have been the case. The simile works to humanize the guards, who are almost entertaining to Billy Pilgrim in this moment when, for the rest of Dresden, the world is burning. The juxtaposition between the people sheltering in the slaughterhouse, and the people burning alive in the rest of the city, makes the simile somewhat absurd: how could Pilgrim think of a barbershop quartet in this moment? A major throughline of the text, however, is that suffering is an inevitable part of life during which one should think of happier moments. This perspective on life, articulated by the Tralfamadorians, is being enacted by Billy Pilgrim as he thinks of a barbershop quartet while looking at his Nazi captors.
It is worth noting that this moment is also one of verbal irony, as the prisoners and guards are some of the only people to survive the Dresden bombing despite sheltering in a slaughterhouse. This irony contributes to the jocular tone of the scene, which clashes with the seriousness of the bombing. Overall, the verbal irony and the barbershop quartet simile alike both evidence Pilgrim's unique perspective on how to cope with the horror of war, one inspired by the Tralfamadorians.