From the rec.humor.funny archives (it has its own page). Attributed to Gary Ericson (GARYE@MAX.ACS.WASHINGTON.EDU").
A biology graduate student went to Borneo to take some samples for his thesis work. He flew there, found a guide with a canoe to take him up the river to the remote site he where he would make his collections. About noon on the second day of travel up the river they began to hear drums. Being a city boy by nature, the biologist was disturbed by this. He asked the guide, "What are those drums?" The guide turned to him and said, "Drums OK, but VERY BAD when they stop."
Well the biologist settled down a little at this, and things went reasonably well for about two weeks. Then, just as they were packing up the camp to leave, the drums suddenly stopped! This hit the biologist like a ton of bricks (to coin a phrase), and he yelled at the guide,
"The Drums have stopped, What happens now?"
The guide crouched down, covered his head with his hands and said:
"Bass Solo"