A New Zealand woman who pulled apart a Christmas cracker got more than the party hat and joke she had expected, finding a dead mouse.

Betty Lawrence, a grandmother from the South Island city of Invercargill, made the discovery sitting down to Christmas dinner with 20 relatives, The Southland Times newspaper reported.

"I had said to my granddaughter 'what's the smell' and we couldn't work it out until we pulled the cracker," Lawrence told the newspaper, after finding a dead and partially decomposed mouse.

The discovery curbed her enthusiasm for the Christmas meal. "It ruined my appetite for the rest of the day," Lawrence said.