John the Baptist
Is Hilditch's flashback of going to the opera as a boy with his mother to watch the play a hint of incest between the two? Throwing up the liver in the stuffing may be of psychological significance as well.
This is one of the top hits when I went looking for information on the beheading of John the Baptist. This is the first I learned of the John the Baptist, bulimia and incest association:
http://www.geocities.com/psychohistory2001/johnthebaptist.html