狐憑き Some kitsune are able to possess human beings and cause them to behave in strange ways. Compared with other types of animal spirit possessions, kitsune tsuki is a relatively common form of possession in humans. A person possessed by a fox spirit often develops physical features that appear fox-like, such as sharper teeth or a streamlined, pointy face. For much of Japanese history—until modern medicine was introduced—mental illness and insanity were usually blamed on kitsune tsuki. Read more: http://yokai.com/kitsunetsuki/