The ceremony involved sinking sacrifices into the earth by night .
The ceremony retrieving the decaying remains of pigs that had been placed in the megara of Demeter ( trenches and pits or natural clefts in rock ) , the previous year .
The ceremony involved sinking sacrifices into the earth by night and retrieving the decaying remains of pigs that had been placed in the megara of Demeter ( trenches and pits or natural clefts in rock ) , the previous year .