The breed is known for a very dense double coat that is either smooth or rough. The fur is particularly thick in the neck area, giving it a distinctive ruff or mane appearance. The bluish color extends to the Chow-Chow's lips; this is the only dog breed with this distinctive bluish color in its lips and oral cavity (other dogs have black or a piebald pattern skin in their mouths). Another distinctive feature is the curly tail. Aggression can be one distinctive behavioural characteristic in this breed, though while some are of an aggressive nature, many are known to be easy-going in nature – sometimes adopting an aloof disposition to individuals other than their owners. Aggression when it does appear is often towards other dogs of the same gender, especially Chows. Due to their strong hunting instincts, it is recommended that these dogs stay fenced, leashed, and away from cats and small dogs.