First of all, the joke was in dubious taste, so i apologize in advance. Also, if you are inclined to post anything truly loathsome, please be my guest. I've heard it all.
In Europe, from about the time of the sack of Rome to the present day, the European monarchies and clergy would stir up the population against Jews. They were accused of everything from The Plague to murdering Christan children for their (the Jews') religious rituals.
Thus incited, an angry mob would oftentimes descend on their Jewish fellow-citizens, confined in walled ghettos or rural communities ("shtetels"), and murder the inhabitants. This kind of violence was called a "pogrom", and they usually occurred around Easter-- when the priests were especially rabid in their denunciations.
I found it… what? Curious? Interesting? That Terry LaBan (whose work i admire) would choose to tell this particular kind of story so close to any Christian holiday.