Other forms: cackleberries
Cackleberry is a humorous slang term for a chicken egg. Fancy a nice cackleberry omelet for breakfast this morning, or would you prefer your eggs fried?
Hens are known for the cackling sounds they make. Fruits, such as berries, and eggs, play similar biological roles, as they both have the potential to become new members of the species. Also, people eat berries, and they eat eggs. Nonetheless, the exact reason why this funny little bit of slang exists is unclear. It does go back to at least the 1910s, so if nothing else, it serves as evidence that people have been making up silly names for things for a long time.