The painting on this oenochoe probably represents the ritual performed during Bouphonia, part of a festival in midsummer in Athens, where a working ox was sacrificed to Zeus. As part of the rite, oxen were brought towards an altar, depicted above. The first ox to eat the grain on the altar is selected for sacrifice, and killed. Because to slaughter a working ox is forbidden, this act is considered murder, and the sacrificer immediately must drop the axe and flee. Later, those involved in the sacrifice are acquitted of the "crime". Porphyry, a Tyrian philosopher from the third century AD, describes the origins of Bouphonia using Theophrastus (a philosopher from the fourth century BCE) as his source. The translation of chapter 10 can be found online.
As Porphyry notes, while there are mythical explanations for sacrifices and rituals, there are many causes that people sacrificed animals. Athenians, he writes, "are full of explanations that are not holy. But most of them assign famine, and the injustice with which it is attended, as the cause." In day to day life, the holy is put aside in favor of the practical: slaughtering animals for the gods gives an excuse for the people to eat meat when normally it would be to expensive and impractical.
Rituals could be complexly choreographed processes, occurring at set times and with set motions, in order to achieve piety and high ceremony. This can be seen during Bouphonia, practed once a year on a specific date only in Athens at the Acropolis. The grain must be spread out by the members of a specific family, and the slaughter of the ox performed by a member of a different specific family (Kentriadae and Thaulonidae, respectively). As seen on the previous page, ritual sacrifice could occur casually, as part of an everyday meal. They could also, as during Bouphonia, be much more involved, casting the eating of the meat after the ceremony as an incidental occurence. Animal sacrifice could be treated in numerous ways and performed under varying circumstances.