Original: Jewelers and silversmiths traditionally use cuttlebones as moulds for casting small objects but they are probably better known as the tough material given to parakeets and other caged birds as a source of dietary calcium.
Simplified: Cuttlebones are traditionally used by jewelers and silversmiths as molds for casting small objects. They are probably better known today as the tough material given to parakeets and other pet birds as a source of calcium for their diets.