Communication in animals is usually not symbolic, and the arbitrariness of signs is typically considered the distinguishing factor between human and animal communication.[29] However, research into great ape language has involved teaching chimpanzees, bonobos, gorillas, and orangutans to communicate with human beings and with each other using sign language, physical tokens, and lexigrams (Yerkish), which contain some elements of arbitrariness. Some also argue that certain animals are capable of symbolic name usage.