A known phenomenon, when a member of the Mortalfolk lacks sleep, their can occur a strange bridge of worlds, enabling the drowser to peer into a world parallel to yet separate from the norm on the surface of the Auld. This realm is different from that of dreams, which opens a portal inside one's own head. In this sleepy state the mortal is still very much conscious. Drifting into this inbetween allows the sight of lost spirit-souls to become possible. These are known as Shades and have no aether, form of being, or known influence on the world.
There is no way to know what state of sleepiness triggers the transition into a separate field of vision. Some claim they were only yawning and yet a traced outline appeared before them. With no way to prove what one has seen, it is a nigh impossible subject of study for intrigued scholars. To date, no communication from a living mortal to a shade or vice-versa has been possible. Even from reports of those having seen the mouth of lost souls move, no sound could be heard and the living's presence appears to go unnoticed.
There will of course be those who insist some form of communication was possible, that they had succeeded in interacting with the world beyond the veil, but such claims are often fantastical and easily dismissed, belonging most likely instead to the realm of dreams.
Should the rumors prove true that Anima Seele exists, a connection could be made to the presence of these "lost souls". Anima Seele is a mythic orb of light that captures souls of the deceased and reincarnates them in tune with the cycle of mortal life upon the Auld. Said to be a creation by The Man With The Clockwork Face, it is not inherently infallible, as no perfect god exists, so must all creations contain the chance of flaws. These souls leftover past death could have been missed by Anima Seele--or possibly rejected, thereby turning into these shades.