Myomancy is a branch of Theriomancy or Zoomancy that deals with predicting the future by interpreting the appearance and behavior of rats or mice.
Derived from the Greek mus ('mouse') and manteia ('prophecy')
In myomancy, omens were predicted by interpreting the noise of the mice. The cries are usually interpreted as bad omen. Another method involved setting a caged mouse free and predicting the future based on the direction or manner in which the mouse escaped. Other diviners free the mouse inside a constructed maze and read auguries depending on the route that it had taken. Predictions can also be made by reading a rat's dropping patterns.
Myomancy was cited in Isaiah 66:17: “Their particular cries or some marked devastation committed by them was taken for a prognostication of evil”.
Claudius Aelianus revealed that Fabius Maximus stepped down from dictatorship because of a warning from rats while Varro claimed that Cassius Flaminius retired from command of the cavalry due to the same reason.
Myomancy was also practiced during ancient Egypt, Rome and Assyria. A rat's cry is believed to indicate the presence of evil. According to Herodotus, when King Sennacherib of Assyria invaded Egypt, his soldiers were attacked by mice and their quivers and bows were gnwaed into pieces. The next morning, his soldiers fled unarmed and were slain.