The mood of “A Perfect Day of Bananafish” starts out fairly light. The initial description of Muriel in her hotel room is dry, detailed, and funny. However, the story is quickly overcome by a sense of melancholy.
Muriel's conversation with her mother reveals them both as shallow, preoccupied with trivial judgments—and yet, Muriel is in a potentially threatening situation, honeymooning with her unstable husband who seems to hate her. Muriel's mother's allusions to things Seymour has done in the past introduce a sense of foreboding. At the same time, though, Sybil and Seymour’s interaction as they look for the fantastical bananafish is whimsical. Still, the strangeness and isolation the reader has already been primed to see in Seymour permeates the conversation. The juxtaposition between Sybil’s blithe innocence and Seymour’s depression and power over her as an adult casts a sinister pall over the scene.
The reader’s unease grows with Seymour’s erratic behavior in the elevator, where he frightens the woman whom he accuses of looking at his feet. Readers don't understand exactly what motivates him but can sense his frustration and his inability to communicate or connect with anyone. When Seymour shoots himself over his sleeping wife, the uneasiness peaks into horror. Overall, the mood conveys a deep disillusionment and despair.