A Maze Mouse is an ordinary-looking mouse, small and slender, its fur the slate grey of the Maze’s stone, sometimes with a rusty tinge like its iron. Its eyes are black and bright and catch the orange of the magma veins. Its whiskers are long, longer than a house mouse’s, and always moving. It runs in short dashes along the foot of a wall and vanishes into cracks no wider than a finger. It squeaks softly, and its tiny feet patter in the Maze’s grinding groan. It smells of dust and damp earth.

They live inside the walls themselves, in the cracks and seams that the Maze’s shifting opens and closes, throughout the zone, and come out into its corridors to forage.

Maze Mice live on what travellers drop and on the fungi that cling to the walls. They feel the stone moving before it moves and run ahead of it, always towards where an opening is about to be, and a mouse in a corridor runs, sooner or later, towards the way out. They are timid but not fearful of people who sit still and offer food, and a fed mouse will stay near.

They read the Maze’s movement through their whiskers and feet, as the Stone-Walkers are said to listen to the stone. More useful still, they have no plan the Maze can foresee, and neither does a traveller who simply follows one.

They breed in nests deep in the walls, and the young learn the stone from birth. When the Maze closes a crack with a nest in it, the mice are already gone. They live short lives, as mice do.

For travellers they are a way out. Experienced travellers carry crumbs, sit quietly until a mouse comes, feed it, and follow it when it runs, without trying to work out where it is going. It is the zone’s own lesson in small: stop trying to solve the Maze. The Stone-Walkers tolerate the mice and the Door-Keepers ignore them, though some say a mouse can lead a traveller past a Door-Keeper’s toll.

Travellers say a mouse will lead only those who feed it, and that one who follows a mouse unfed is led deeper in; this is said to teach manners, and is probably untrue. In caves and ruins near the Rock-Gates that open on the Maze, miners and children are told that if they are lost underground they should follow a mouse, which is sometimes good advice anywhere.

Treasure-seekers carry a bag of crumbs into the Maze before they carry a map, and the story of the delver who came out following a mouse with a sack of gold on his back and no companions is told both as a lucky tale and as a cruel one.