The initiation, myesis, was an act of individual choice. Most but not all Athenians were initiated. Women, slaves, and foreigners were admitted. The first act was the sacrifice of a young pig.
Burkert establishes the Eleusinian initiation as a voluntary, socially inclusive individual rite whose foundational gesture is substitutionary pig-sacrifice, not agrarian magic.
, Greek Religion: Archaic and Classical, 1977thesis