In Irish and Scottish folklore, the Sluagh were the spirits of the restless dead. Sometimes they were seen as sinners, or generally evil people who were welcome in neither heaven nor hell, nor in the Otherworld, who had also been rejected by the Celtic deities and by the earth itself.
Whichever the underlying belief, they are almost always depicted as troublesome and destructive.
They were seen to fly in groups like flocks of birds, coming from the west, and were known to try to enter the house of a dying person in an effort to carry the soul away with them. West facing windows were sometimes kept closed to keep them out. Some consider the Sluagh to also carry with them the souls of innocent people who were kidnapped by these destructive spirits.