Extispicy in Mesopotamia was a learned craft rather than a spontaneous inspiration. A baru trained for years memorizing the Baru omen series, thousands of entries each recording a specific liver feature, a fissure in a particular lobe, an unusual gall bladder shape, a mark on the presence of the god, alongside the historical or personal outcome it was believed to portend. Clay models of sheep livers, some marked with the anatomical zones diviners named and others inscribed with the omens themselves, functioned as both teaching aids and durable references, and examples survive from Old Babylonian Mari and elsewhere going back to the early second millennium BCE.
Before the sacrifice, the baru formally addressed Shamash and Adad, posing the specific question to be answered as a yes or no proposition, since Mesopotamian extispicy was fundamentally a binary consultation technique, not an open ended prophecy. The animal was then killed and its organs examined feature by feature against the trained catalogue, with unfavorable and favorable signs weighed against one another to reach a final verdict. Some clay liver models carry a short written verdict alongside the anatomical marking they illustrate, letting modern scholars reconstruct not just what a baru looked for but the specific historical judgment a particular configuration was once recorded as having produced.