In the first chapter, when discussing the difficulty that he had writing the anti-war novel, Vonnegut explains that "there is nothing intelligent to say about a massacre." Since the bombing of Dresden is a massacre, there is nothing intelligent to say about it. Since the last scene of the novel occurs shortly after the bombing of Dresden, Vonnegut ends with a nonsensical and unintelligible question: "Poo-tee-weet?"
By ending the novel this way (by asking a question that makes no sense), Vonnegut drives home the point that war makes no sense and that the bombing of Dresden was a senseless act. Furthermore, "Poo-tee-weet?" is a question and not a statement of fact. Thus, Vonnegut ends with a nonsensical question that the reader cannot answer intelligibly, and the reader is in a similar situation as Vonnegut, who can find "nothing intelligent to say about a massacre."
Finally, as Vonnegut states in the opening chapter, it is the birds that ask this closing question.
"Everything is supposed to be very quiet after a massacre, and it always is, except for the birds. And what do the birds say? All there is to say about a massacre, things like "'Poo-tee-weet?'"
Humans are the only animals capable of such destruction, and the birds are left to question this horrific act. Throughout the novel, Vonnegut shows that animals are innocent victims of war as seen in the wounded horse that Billy weeps for and in "Princess," the dog with its tale between its legs, who has been dragged into the war.