Explain the irony of the title behind the story "Lamb to the Slaughter."

The irony in the title of Roald Dahl's story "Lamb to the
Slaughter" has to do with the tension between the literal and figurative meanings of the
phrase in the title.  At the beginning of the story, the main character Mary Maloney is
trying to put together dinner for her husband Patrick.  She tells him that she has taken
out a leg of lamb for dinner, but he does not really care.  Shortly after, Patrick tells
Mary that he is leaving her.  By this point it is obvious that there have been problems
in the marriage, and Mary clubs Patrick over the head with the leg of lamb--so she
literally "slaughters" him with the lamb.  However, figuratively, the phrase alludes to
the loss of innocence that occurs when people reach certain stages of life.  The lamb
has been used throughout literary history to represent innocence and the slaughter to
represent the moment when that is lost.  Mary suggests that her husband has not been the
best partner for her, so it is also ironic that he decides to leave
her.  Mary loses her innocence when she takes his life and has to
then try to cover up her crime and atone for her actions.