What kinds of irony can be found in "Lamb to the Slaughter"?

can
be:

• Situational: actions result in a different outcome than
  expected
• Verbal: sarcasm; when words mean the opposite of what they
  originally intend to mean
• Dramatic: actions and events understood by the
  audience, but not the characters

All three examples of irony are
evident in "."

The verbal irony is
found in the title of the story. The phrase "Lamb to the Slaughter" suggests an
innocent creature about to undergo torture and death. Mary Maloney could represent such a
creature, and she would have met a similar fate if she had been found guilty of killing her
husband.

More verbal and situational irony is
represented in the murder weapon and what happens to it, unbeknownst to the people investigating
the scene of the crime.

The murder weapon is a frozen leg of lamb. Mary hits
her husband with it after mentally "snapping" when he announces to her that he will
leave her. The hit kills him instantly. Shortly after, Mary comes up with a way to dispose of
the murder weapon: she cooks it. What's more, she feeds it to the policemen who come to
investigate the scene.

As the audience, we know what is going on.The
characters do not. That would be the dramatic irony. We realize
that they are eating the very thing they need to find in order to apprehend the person guilty of
killing their fellow policeman, Patrick Maloney. They even comment that the murder weapon could
be right "under their noses," which it is.  

Meanwhile, in the
other room, Mary Maloney giggles at the situational irony of it
all. The lamb, after all, saved her from the slaughter of what could have been a death sentence,
or life in jail as a pregnant woman.