The sacrifice of the month is entirely dependent on the Eternal Meepism of the Month, a piece of wisdom which the religious leaders of the Followers, the Great Meepers, claim to recieve from a jellyfish formation in the Great Sea of Meep, which is in the parallel Holy Meep Dimension, at the heart of which the Great Meepismor resides. Only the very Meepest can enter the Holy Meep Dimension, according the the Great Meepers.
When the Eternal Meepism of the Month has been revealed, preparations for the Sacrifice, which takes place the day before the revealing of the next Eternal Meepism, begin. If the Meepism is a happy one, a jellyfish is sacrificed by the Great Meepers themselves. If it is not pleasant, a human is sacrificed, using the stings of jellyfish. The human to sacrifice is chosen by the Great Meepers, depending on who they feel it would most please the Eternal Meepismor to sacrifice. The method of sacrifice is supposed to keep the balance - jellyfish are sacrificed by humans; humans are sacrificed by jellyfish.
Studies proving a strong correlation between Great Meepers whose PMS coincides with the Choosing of the Meepism and the proportion of sacrifices which are human is largely disregarded, because people who pay attention to it have a mysterious tendency to end up as the next sacrifice.
As previously stated, only the Meepest can ever enter the Holy Meep Dimension. Therefore, only the Meepest know that it actually exists. Only the Great Meepers have the power to Percieve the Meepness of others, and they always seeem to declare themselves much more Meep than others. Those who the Great Meepers declare truly Meep often tend to be those whose bank accounts' sudden decline coincides with the sudden rise in the Great Meepers'. People who investigate this principle often tend to meet the same fate as the PMS investigators.