"Boo!" was inspired by the release of the newest Harry Potter book.

Cardinal Ratzinger (a few months before being elected Pope) condemned
the Harry Potter books saying they could potentially corrupt children.

A school in England canceled a "Harry Potter Day" after a local pastor and
some parents raised concern because of the book's ties to witchcraft.

All of this could lead one to think back to the Salem Witch Trials in the 17th 
century. There is strong evidence that the hysteria, hallucinations and tremors 
of the accused 'witches' was caused by ergot poisining. Ergot is a fungus 
that infects rye - a staple food in the diet of the people of Salem. (The witch 
in the painting "Boo!" is holding stems of a rye plant.)