The Mourners | Of Ash and Iron

In the burned villages, the dead do not lie down. They stand as their last moment caught them — reaching for doors long burned away, shielding children that are ash now. Hollow shells of cinder, each keeping the one small spark the fire could not finish. The hunters call them Mourners. Pity them, if you must. Then put them out.

From the ledgers of the Order of the Tamed Flame:
"It chooseth not the meanest shell, but the best-kept: one wherein the bones stand true. Through the hollow of the back it entereth, and maketh its seat within the spine, and thereafter doth remake each bone in its own order, joint by joint, as a mason taketh down a steeple and buildeth of the same stones a gallows. What the vessel suffereth in that hour, no man knoweth. Yet this much the watch-brothers attest: even a shell long emptied of soul and substance will, at the remaking, give forth a cry. And they that have heard it do not write of it, save to say — pray thou never learn what is left within, that it should mourn so."

the Mourners are built on the Pompeii casts - hollow cinder shells frozen in the pose of their last second, with a single ember as the danger tell (dim shell is a grave, bright one is a womb). The Mournsnake is no outside demon: everything the worm is made of was already in the man. It roots into the spine and puppets the shell through rib-strings.