"The Devil's Mouthful" is an idiom in the English language for the consequence of fraud. It comes from George Meredith's 1859 novel "The Ordeal of Richard Feverel", when, in a book, beside the aphorism "The dog returneth to his vomit: the Liar must eat his Lie," the protagonist of the story's father writes, "The Devil's mouthful!"
Now very infrequently used, this turn of phrase is of relative interest because it has intentional moral undertones. It equates the liar to a dog, lowering his status to that which is decidedly sub-human; it implies that while a man can transgress and proceed, a dog (and maybe anything less than human) must return to his mistakes. This is then to say that the nature of the lie is particularly defiling, moreso than, at the very least, another sort of transgression, and that it is among the sorts which never decay. This notion is probably, for the most part, a historical one; it is, however, wonderfully telling of 19th century society.