Causing invisibility by means of a spell called _feth fiada_, which made a person unseen or hid him in a magic mist, was also used by the Druids as well as by Christian saints. S. Patrick's hymn, called _Fâed Fiada_, was sung by him when his enemies lay in wait, and caused a glamour in them. The incantation itself, _fith-fath_, is still remembered in Highland glens.[1109] In the case of S. Patrick he and his followers appeared as deer, and this power of shape-shifting was wielded both by Druids and women. The Druid Fer Fidail carried off a maiden by taking the form of a woman, and another Druid deceived Cúchulainn by taking the form of the fair Niamh.[1110] Other Druids are said to have been able to take any shape that pleased them.[1111] These powers were reflected back upon the gods and mythical personages like Taliesin or Amairgen, who appear in many forms. The priestesses of Sena could assume the form of animals, and an Irish Circe in the _Rennes Dindsenchas_ called Dalb the Rough changed three men and their wives into swine by her spells.[1112] This power of transforming others is often described in the sagas. The children of Lir were changed to swans by their cruel stepmother; Saar, the mother of Oisin, became a fawn through the power of the Druid Fear Doirche when she rejected his love; and similarly Tuirrenn, mother of Oisin's hounds, was transformed into a stag-hound by the fairy mistress of her husband Iollann.[1113] In other instances in the sagas, women appear as birds.[1114] These transformation tales may be connected with totemism, for when this institution is decaying the current belief in shape-shifting is often made use of to explain descent from animals or the tabu against eating certain animals. In some of these Irish shape-shifting tales we find this tabu referred to. Thus, when the children of Lir were turned into swans, it was proclaimed that no one should kill a swan. The reason of an existing tabu seemed to be sufficiently explained when it was told that certain human beings had become swans. It is not impossible that the Druids made use of hypnotic suggestion to persuade others that they had assumed another form, as Red Indian shamans have been known to do, or even hallucinated others into the belief that their own form had been changed.