Again, although the barbershop quartet only appears in a few places in the novel, it is an important link between the worlds Billy Pilgrim inhabits—in which he is “stuck” and “unstuck.” Billy does not understand why, during his and Valencia’s wedding anniversary party, he is shaken by the sight of four men singing together. Later these four men will sing on the plane that, in crashing, nearly kills Billy and sets off, indirectly, Valencia’s death. Only after remembering—not traveling through time—does Billy see that the barbershop quartet resembles the four German soldiers standing together, along with the 100 US POWs, in the slaughterhouse during the bombing. Kilgore Trout picks up on the importance of this connection, claiming he knows that Billy is seeing through a “time window.” And indeed the quartet triggers a cascade of connections between Billy’s past in the war, his violent life afterward, and his investigations of time under the influence of the Tralfamadorians.