Later, she won't be able to say when, exactly, she snapped.
She's not like most of the slaves here. Morgana hasn't been able to break her. Hasn't been able to override her, not with the pleasure of the Singing Light nor the fear of digestion nor simple force. Her worms can enter Shendi's body, but not her mind.
That's made her valuable. Almost sheltered, really. The Humming Lord breaks a thousand slaves, and Shendi endures, and Shendi listens.
(There's another thing that makes her valuable. The Humming Lord is blind, as are all her people, her slaves, her things. As is Shendi. But while the worms can hear the faintest vibration from across the Sands, they cannot hear what Shendi does. Perhaps no one can.)
She listens, impassionate, as new captives are thrown in the spawning pits, to be nests or food for the ever-churning mess of juvenile worms, to be tested and raped and broken. She listens, and she sorts through them. Identifies who is useful, who is convenient, who is merely flesh.
She listens, impassionate, to the movement of the great tunnelers through the sandstone. She listens to the distant hum of people like she once was, slaves who don't know it yet, and she answers Morgana's questions in a dull voice.
She listens, and so she hears first when something changes.