This excerpt is from Book II, concerning Plato's reasoning for censoring a certain story of Hesiod's:
The doings of Cronus, and the sufferings which in turn his son inflicted upon him, even if they were true, ought certainly not to be lightly told to young and thoughtless persons; if possible, they had better be buried in silence. But if there is an absolute necessity for their mention, a chosen few might hear them in a mystery, and they should sacrifice not a common [Eleusinian] pig, but some huge and unprocurable victim; and then the number of the hearers will be very few indeed.
Is the sacrificing of the pig metaphorical or literal? Of what significance is the word Eleusinian? Who is the huge and unprocurable victim? What is the connection between the bolded portion with the rest of Plato's argument?