"Lamb to the Slaughter" Mary's Giggling

At the end of “Lamb to the Slaughter” by Roald Dahl, Mary Maloney begins giggling because the policemen were trying to find the weapon, but what they didn't know was that they were eating it. Mrs. Maloney killed her husband with a piece of lamb by wacking it to his head. She put the big piece af meat in the oven so it would look like she didn't kill him. When the policemen were searching aroud for a big club they didn't suspect it to be the meat. After the police leave the house, I predict Mary will have a melt down and repeat the same thing with other guys that would leave her.