Read quickly, the poem sounds like a small, elegant moment: a woman puts on a necklace to mark the day someone died. But the last two lines change everything. "The police still have no idea" suggests she is hiding something, and the death was no ordinary loss. The poem hints, without ever saying so, that she may be responsible.
What makes it unsettling is how calm it is. Nothing in the language is dramatic. The short lines move slowly, almost like a ritual, and the speaker never raises her voice or explains. We get no sense of guilt or panic, only composure, maybe even satisfaction. The black pearls work as a kind of private memorial, or a private joke, worn in plain sight where no one can read them.
The mood is cool, secretive, and darkly witty. The poem lets us in on a secret the police can't see, which makes us feel slightly complicit.