The Maine Coon is a large and sociable cat, hence its nickname, "the gentle giant". It is characterised by a prominent ruff along its chest, robust bone structure, rectangular body shape, an uneven two-layered coat with longer guard hairs over a silky satin undercoat, and a long, bushy tail. The breed's colors vary widely, with only lilac and chocolate disallowed for pedigree. Reputed for its intelligence and playful, gentle personality, the Maine Coon is often cited as having "dog-like" characteristics. Professionals notice certain health problems recurring in the breed, including feline hypertrophy cardiomyopathy and hip dysplasia, but reputable breeders use modern screening methods to minimise the frequency of these problems.