She sits and hums. It isn’t a recognisable tune. A hymn to her inner workings, perhaps. The movement of her mind sent out into the world through vocal vibrations. She sits and hums and fills the bus with the sound of herself, low level, barely audible, just loud enough to be noticed when she stops.

When she stops, it’s to breathe. Slight inhalation to refresh the humming exhalation. The gasp that opens her mouth lets out the smell of decaying teeth. A particular smell, sweet and musty, not unpleasant until it suddenly is.

The volume of her hum alters with the movement of her head. It deadens when she turns to look through the window, as though the tempered glass has sound absorbing properties. But that breaks the laws of physics, and something else must be muting the sound. Perhaps the fake fur collar of her leopard print coat, so inappropriate on this warm summer day. Or the twist in her neck restricting her vocal chords.

Whatever it is, it stops when she turns back to face forward, and her humming becomes momentarily louder again. The passengers’ ears adjust. The humming seems softer. It is almost soothing, and yet unsettling.