Lagniappe: "The old sweet song," said Holmes.

"If it takes me all my life I shall get level with you!"

"The old sweet song," said Holmes. "How often I have heard it in days gone by. It was a favourite ditty of the late lamented Professor Moriarty. Colonel Sebastian Moran has also been known to warble it. And yet I live and keep bees upon the South Downs."

Arthur Conan Doyle, The Last Bow

Just because it is delightful. Which is how lagniappe works!