Haitian ritual drumming is the tradition's most technically demanding knowledge and it is entirely unwritten. The ensemble of manman, segon and boula plays interlocking patterns specific to each nanchon and to individual lwa, so that the rhythm identifies who is being addressed. The manman drummer leads and executes the kase, the break — a calculated interruption of the pattern, directed at a specific dancer, which disrupts the entrainment and is understood as the technical means by which possession occurs. Drums are consecrated and have ceremonies of their own; drummers train from childhood and the most accomplished are known nationally. Haitian ritual drumming has fed directly into Haitian popular music, into the rasin movement of the 1980s and 1990s, and into the wider Caribbean and American percussion traditions, generally without acknowledgement of the source.