A slip-fox is a slim red fox the size of a small dog, with a fox’s narrow muzzle, black stockings, and white-tipped brush. Its coat is paler than a common fox’s, a washed-out red with a grey sheen, as if seen through mist, and its outline is never quite sharp. When it slips, it does not vanish at once: it thins, like breath on glass, and goes, and when it returns it seems to step out from behind nothing. Its eyes are amber and catch the light more than they should. It barks and screams like any fox, and for a moment after it slips the bark seems to come from a long way off. It smells of fox and, faintly, of wet fog.

They den in banks and ruins near thin places, and range along the roads and boundaries around them. Where a thin place is strong there may be several families; away from thin places slip-foxes are not found.

They hunt mice, birds, and beetles like any fox and steal from shrines and travellers' packs. A slip-fox that is chased slips, and comes back behind the chaser; one that is curious follows travellers for a mile or more, stopping and looking back. It is wary and clever, and it seems to enjoy being followed.

It can step partway into the Veil and out again, crossing a short distance unseen, and it is never lost there, as a fox is never lost in its own woods. It does not go far in, or for long.

They breed as foxes do, a litter in spring, and the cubs are said to learn to slip in their first summer, at play. They live a few years.

They give nothing, and do little harm by themselves beyond the stolen offering and the dead hen. The danger is the following. A traveller who goes after one, off the road, without a clear aim, is led into the edge of the Veil and can lose the way entirely; guides tell of children found days later and miles away, and of some never found. Hunters with dogs lose their dogs.

Human folk call them "the Veil’s own dogs" and say they lead the dead home, or lead the living astray for the fun of it. Travellers are told never to follow a fox at a shrine, and to say aloud where they are going when they see one. Some believe a slip-fox caught and kept will show its keeper the way through; those who try keep it a few days, and it slips. Whether they were foxes changed by the thin places or have always been as they are, nobody knows.

Smugglers and outlaws are said to follow them on purpose, trusting the drift to shake off pursuit, and the boundary-road songs tell of a bandit chief who followed a slip-fox out of a lord’s net and came out of the fog a year later, in another country, with the noose still round his neck.