Deuteronomy 19:16

Transgression against the law, by apostacy or by idolatry, (Junius) or by any other grievous crime. The person accused might, in this case, be examined, but he could not be condemned unless another witness appeared. Demosthenes (contra Aristocrat.) informs us how (Calmet) the Athenians (Haydock) required the witness in criminal matters, to swear on the flesh of a wild boar, ram, and bull, that he spoke the truth, and to utter horrible imprecations against himself and family, if he did otherwise. (Calmet)