Myomancy was a method of theriomantic divination by rats or mice, which may be alluded to in Isaiah 66:17. Their particular cries or some marked devastation committed by them was taken for a prognostication of evil.
Ælain relates that Fabius Maximus resigned the dictatorship in consequence of a warning from these creatures; and Cassius Flaminius, according to Varro, retired from the command of the cavalry for the same reason. According to Herodotus, when Sennacherib invaded Egypt his army was infested by mice in the night, and their quivers and bows gnawed in pieces; in the morning, therefore, being without arms, they fled in confusion, and many of them were slain. Such a foreboding of evil could not very well be questioned, or its consequences averted, by the commander. The outcome was rather different when one of Cato's soldiers told him in fright that the rats had gnawed one of his shoes. Cato replied that the prodigy would have been much greater if the shoe had gnawed a rat.
Horapollo describes the rat as a symbol of destruction. The Hebrew name of this animal is from a root which signifies to separate, divide, or judge; and it had been remarked by one of the commentators on Horapollo that the mouse has a finely discriminating taste.
An Egyptian manuscript in the Bibliothèque nationale de France in Paris contains the representation of a soul going to judgement in which one of the figures is depicted with the head of a rat and the well-known wig. The Libyan rats and the mouse of the Old Testament are the same as the Arabian Jerboa, which is characterized by a long tail, bushy at the end, and short forelegs.