A cuttlebone is not actually a bone, but rather the internal shell of the Cuttlefish, a small, squid-like cephalopod. In the Cuttlefish, the cuttlebone is filled with gasses and helps control the fish's buoyancy in the water. While for years people have harvested and used cuttlebones for various purposes, the most widely recognized use of the cuttlebone is as a supplement and exercise toy for birds.
In traditional medicine, cuttlefish bone has salty and warm properties, and is associated with the Kidney, Liver and Stomach meridians. Its functions are to stop bleeding, harmonize the stomach and improve kidney deficiency. Internally, it is taken to help stop bleeding of the uterus, enuresis and premature ejaculation. Some patients with stomach problems may take it to combat acid reflux disease and some intestinal disorders. Topically, cuttlefish bone can be used as a poultice to treat skin rashes, ulcers and lesions.
Beside that the cuttlebone is a lightweight, oblong, chalky object that is mainly composed of calcium -- making it an ideal way to supplement a birds's calcium intake.
Cuttlebones have a grainy texture, reminiscent of pumice. This texture can also offer benefits to parrots as it is helpful in wearing down overgrown beaks. It's recommended to always keep a cuttlebone in your bird's cage to promote beak and jaw exercise.