From Lady Wilde, Ancient Legends of Ireland, pages 29-30:
he evil influence of the fairy glance does not kill, but it throws the object into a death-like trance, in which the real body is carried off to some fairy mansion, while a log of wood, or some ugly, deformed creature is left in its place, clothed with the shadow of the stolen form. Young women, remarkable for beauty, young men, and handsome children, are the chief victims of the fairy stroke. The girls are wedded to fairy chiefs, and the young men to fairy queens; and if the mortal children do not turn out well, they are sent back, and others carried off in their place. It is sometimes possible, by the spells of a powerful fairy-man, to bring back a living being from Fairy-land. But they are never quite the same after. They have always a spirit-look, especially if they have listened to the fairy music. For the fairy music is soft and low and plaintive, with a fatal charm for mortal ears.One day a gentleman entered a cabin in the County Clare, and saw a young girl of about twenty seated by the fire, chanting a melancholy song, without settled words or music. On inquiry he was told she had once heard the fairy harp, and those who hear it lose all memory of love or hate, and forget all things, and never more have any other sound in their ears save the soft music of the fairy harp, and when the spell is broken, they die.
It is remarkable that the Irish national airs--plaintive, beautiful, and unutterably pathetic--should so perfectly express the spirit of the Ceol-Sidhe (the fairy music), as it haunts the fancy of the people and mingles with all their traditions of the spirit world. Wild and capricious as the fairy nature, these delicate harmonies, with their mystic, mournful rhythm, seem to touch the deepest chords of feeling, or to fill the sunshine with laughter, according to the mood of the players; but, above all things, Irish music is the utterance of a Divine sorrow; not stormy or passionate, but like that of an exiled spirit, yearning and wistful, vague and unresting; ever seeking the unattainable, ever shadowed, as it were, with memories of some lost good, or some dim foreboding of a coming fate--emotions that seem to find their truest expression in the sweet, sad, lingering wail of the pathetic minor of a genuine Irish air. There is a beautiful phrase in one of the ancient manuscripts descriptive of the wonderful power of Irish music over the sensitive human organization: "wounded men were soothed when they heard it, and slept; and women in travail forgot their pains." There are legends concerning the subtle charm of the fairy music and dance, when the mortal under their influence seems to move through the air with "the naked, fleshless feet of the spirit", and is lulled by the ecstasy of the cadence into forgetfulness of all things, and sometimes into the sleep of death.