Prediction from the entrails of animals, referred to as haruspicy, is an ancient system that went out of fashion about two thousand years ago, much to the relief of the world's sheep and goat populations. In the haruspical heyday of the Roman Republic and Empire, battalions of animals were sacrificed to the divinatory cause.

Haruspicy is derived from a very early form of soothsaying known as hepatoscopy, or "liver gazing," particularly popular among the Babylonians, and Etrurians, who believed that it had been bestowed upon them by one of Jupiter's grandsons, Tages.

Both haruspicy and hepatoscopy proceed along the same basic principles. Following the ritual sacrifice of some largish animal -- sheep, calves, bulls,  and goats were preferred -- the haruspex (diviner) slit open its belly to inspect its entrails. Even in the multi-organ exegesis of haruspicy, the liver was the key; the pattern of its veins and the variations of its colors were examined and interpreted according to their resemblance to the signs associated with the gods. The gallbladder, too, was important. A particularly swollen gallbladder foretold military triumph; deflated, it predicted disaster.

The Romans were originally suspicious of haruspicy, seeing it as just the kind of backwoods divination you would expect from an Etruscan. They preferred their native form of divination, augury, or prediction by omens. The problem was that their omen of choice -- the flight of birds -- was unwieldy, and, as time went on, the Romans turned to haruspicy. Generals in the midst of battle, especially, needed a quick method of consulting the gods and found entrails most convenient. In the last years of the Republic, a haruspex was included on the staff of every commander-in-chief and was habitually consulted on military strategy.