The Sluagh (sloo-ah) are the restless spirits of the deceased. Thought to be sinners, they were not welcome in heaven, hell, or the otherworld.
These lost spirits fly in flocks, similar to birds, and approach from the west. Creatures of destruction, they wait until nightfall, then try to enter the home of a dying person. Entering like a shadow, they carry off with the soul of the dying person in a flurry of wings and screeches.
The most vulnerable to the Sluagh are those in despair or suffering from loss. Broken hearts would call them to their doorstep.
While the Sluagh are considered departed miscreants, sometimes they’d kidnap innocent souls for the challenge. Therefore, it was common practice to keep the west-facing windows closed if someone was near death.
However, once the sluagh identified a victim, the only escape was to offer another in their stead. A horrible prospect, because the act of sacrificing someone in your place, could guarantee you join their ranks.