E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
May this piece of bread choke me, if what I say is not true. In ancient times a person accused of robbery had a piece of barley bread, on which the mass had been said, given him to swallow. He put it in his mouth uttering the words given above, and if he could swallow it without being choked, he was pronounced innocent. Tradition ascribes the death of the Earl Godwin to choking with a piece of bread, after this solemn appeal. (See CORSNED.)