The music of Zambia has a rich heritage which falls roughly into categories of traditional, popular and Christian music. Traditional music Traditional Zambian music is rooted in the beliefs and practices of Zambia's various ethnic groups and has suffered some decline in the last three decades. Traditional Zambian music once had clear ritual purposes or was an expression of the social fabric of the culture. Songs were used to teach, to heal, to appeal to spirits, and for mere enjoyment. Despite the decline of traditional music, its influences can still be heard in many of today's Zambian musical forms. The ubiquitous African "call-and-response" can be heard in almost every Zambian song no matter what the style. Traditional drum rhythms and polymeters are evident in many different kinds of Zambian music. Contemporary popular forms such as Zambian Kalindula also exhibit traces of traditional music in the finger-picking style used by guitarists. Instruments Traditional Zambian instruments include a variety of membranophones, both stick-struck and hand-struck. Drums are essential for most traditional dances. Ngoma is the generic central Bantu term for drum but Zambian drums come in a variety of sizes, shapes, and purposes and have specific names depending on their tribal origins and functional roles. The Budima drums of the Valley Tonga, for example, are used specifically for funeral ceremonies. Budima drums have a goblet shape and come in sizes ranging from large to small. One of the most interesting of drums is the so-called "lion drum" (Namalwa in Tonga) used at traditional funerals. This is a friction drum which is not struck at all but which has a stick inserted through the drum head that is rubbed. The silimba is a large 17-note xylophone from Western Province. Chordophones and aerophones are less common in traditional Zambian music but exist nonetheless. The Valley Tonga play instruments made from animal horns called Nyeele. Nyeele are played using an interlocking technique with individual musicians each playing a single horn and interlocking with other musicians who have Nyeele of different pitches. A chordophone called a kalumbu was traditionally played by young men to signal their desire to marry. Called a 'musical bow' by ethnomusicologists because of its bow shape, the kalumbu is struck by a stick. Like many other central African countries, Zambia once had a vibrant tradition of so-called "thumb pianos," each with a different name depending on tribal origins: the Tonga kankobela is