http://www.flickr.com/photos/cykuck/3013532141/ Vmbuza is a healing dance. It happens at the traditional healer's compound once a week, usually on a Friday night and lasts all night.
The women play a rhythm with wooden sticks. A couple guys play a second rhythm with hand drums. It's LOUD and it's POWERFUL. The traditional healer led the songs, which I think are partly or wholly improvised and can last 15 or 20 minutes.
The patients dance until they can't dance any more. I have no doubt that it makes people feel better. It makes me feel better every time I go!