The Cù Sìth is a giant spectral dog of Scottish mythology. They were said to be about the size of a cow or large calf, and be bright green in color, with a curled and braided tail and a rough coat. (In Ireland, however, they were said to be coal black with flaming eyes).
The name literally means “fairy dog.” They were said to haunt the Scottish Highlands, and it was said that they were harbingers of death, capable of dragging a soul to the afterlife. They can hunt silently, but also on occasion let out three shrill and terrifying barks which can be heard for great distances—even far out to sea. This is said to be a warning for farmers to “lock up their women,” or the dogs would carry them off to fairy mounds, where they would be used to provide milk for the fairy children.