Sign language is a way to communicate using gestures. They used this sign language to exchange information or to trade with members of culture groups who spoke a different language from their own. Sign language was also used to communicate silently with speakers of the same language during hunting or raiding parties when silence was critical. Plaines culture groups that are known to have used sign language include the Arapaho, Cheyenne, Pawnee, Kiowa, Crow, Osage, Comanche, Pawnee, and the Dakota, Lakota, and Nakota. The Blackfeet and the Assiniboime, also Great Plaines culture groups, used sign language, as did the Plateau tribe the Nez Perce and the Ute of the Great Basin. Sign language was developed to a high degree of sophistication by the Plaines tribes, who used over 1,000 distinct gestures to communicate word or concepts. Fur traders and mountain men who interacted with Native Americans on the Plaines quickly learned sign language in order to communicate with them. Later U.S. soldiers learned the signs.