This section is from the book "Ancient Legends, Mystic Charms, And Superstitions Of Ireland", by Jane Francesca Wilde. Also available from Amazon: Ancient Legends, Mystic Charms, And Superstitions Of Ireland.
Another relic held in reverence for swearing on by an accused person is St. Finian's Dish. This was found about one hundred and fifty years ago, buried in the ruins of an old abbey. It is of silver with stones set in it, which, the people say, are the eyes of Christ looking at them while they swear. And when the dish is shaken a rattling noise is heard, which they believe is made by the Virgin Mary's bones that are enclosed therein.
Should a false oath be taken on the relic, the perjurer will at once be stricken by disease, and die before the year is out. And so great is the terror inspired by this belief, that men have fainted from fear when brought up to swear on it. This is done by placing the hand on the cross that is engraved in the centre of the dish, while the two eyes of Christ are fixed on the swearer who comes for clearance from guilt.
The Ghar-Barra, or Crosier of St. Barry, is also a holy relic once overlaid with gold, on which it was the custom to take a clearing oath ; as the people held it in great reverence, and nothing was more dreaded than the consequence of a false oath on the Ghar-Barra. Once a man who swore falsely thereon had his mouth turned awry, and it so remained to his life's end, a proof of the saint's hatred for the sin of perjury. The relic is kept covered carefully with green cloth, and whoever is brought to take a clearing oath thereon must first lay down a small piece of silver for the guardian of the shrine.