In the lamb to the slaughter how does marys behavior at the grocery shop contradict what has happened earlier in the story

After killing Patrick, Mary decides to go to the grocery shop and acts normally and innocently as if she does not know anything about her husband's murder.

Explanation:

"Lamb to the Slaughter" is a short story written by Roald Dahl published in Harper's Magazine in Sept. 1953.

Mary Maloney is the wife of a detective, Patrick Maloney. She is the main character (or protagonist) of the story. She is a six months pregnant housewife, who is devoted to her husband. She notices some strange behavior in her husband but ignores thinking that he must be tired and gets back to her usual routine. But alter Patrick reveals to her that he wants to leave her. Mary hits Patrick with the frozen leg of lamb which immediately kills Patrick. The killing was not intentional. Mary at first decides to tell the truth to the cops but for the sake of her child, she cleverly tries to cover up her sin. She goes to the grocery shop and talks to the grocer normally as if nothing happened and she does not know anything about her husband's murder.

im not sure about this one

(4) "oh, i've got better plans than that," laughed kerry. "i've got four firecrackers and two model rockets. care to join me in the backyard? "

this is the correct answer because of one simple word. "backyard"