In ancient Pagan times in Ireland the poets were supposed to possess the gift of prophecy, and by certain means could throw themselves into a state in which they had lucid vision of coming events. This state, called Imbas for Osna, was produced by incantations and the offering of the flesh of a red pig, a dog, or a cat to their idols. Then the poet, laying the two palms of his hands on his two cheeks, lay down and slept; his idol gods being beside him. And when he awoke he could see all things and foretell all things. He could make verses with the ends of his fingers, and repeat the same without studying, and in this way proved his right to be chief poet at the court of the king. Also he laid his staff upon the head of a person, and thus he found out his name, and the name of his father and mother, and all unknown things that were proposed to him. And this prophetic power was also obtained by Imbas for Osna, though a different kind of offering was made to the idol.
But Patrick abolished these practices, and declared that whoever used them should enjoy neither heaven nor earth; and he substituted for them the Corus Cerda (the Law of Poetry), in which no offering was made to demons; for the profession of the poet, he said, was pure, and should not be subject to the power of the devil. He left to the poets, however, the gift of extemporaneous recital, because it was acquired through great knowledge and diligent study, but all other rites he strictly forbade to the poets of Erin.