The flesh of the animals which was not used for the sacrifice was usually consumed at the feast which followed the ceremony; this custom was only departed from in the case of sacrifices to the shades of the dead or for purposes of propitiation, and then the flesh which was not burnt was buried or destroyed in some other way, and, in fact, on these occasions many of the ceremonies were of a different kind. As a rule, another purpose was combined with the sacrifice; it was necessary not only to win the favour of the gods, or atone for some crime, but also to discover the will of the gods by interpretation of signs. Although prayer was called for from all men--from labourer as well as from priest--and sacrifices, though usually offered by priests, could also be performed by others, the interpretation of omens was an art which depended on ancient traditions and knowledge of ritual, and was almost entirely confined to the priests, though, in the nature of things, it could be undertaken by anyone. This mode of prophecy had existed in various forms since the most ancient times. The commonest, though unknown in the time of Homer, was the examination of the entrails, in which the structure, that is, colour, form, and integrity of the inner parts of the victim, especially the liver, gall, etc., were regarded as of fortunate or unfortunate omen. Some anatomical knowledge of the inner parts of animals was therefore indispensable, and in consequence it is natural that this branch of knowledge was kept in the hands of the priests. The older kind of prophecy described in Homer was of a different nature, since it depended on all manner of phenomena appearing during the sacrifice; whether the flame attacked the victim quickly or slowly, whether it burnt clearly, whether it rose upwards, whether it was not put out until the whole animal was consumed, whether the wood crackled loudly, what shape was assumed by the ashes of the victim and of the wood, etc.