What do you call a drummer up to his neck in concrete? Not enough concrete.

A scientist on an expedition disembarks from his plane at the final outpost of civilization in the deepest Amazon rain forest. he immediately notices the ceaseless thrumming of native drums. As his party ventures further into the bush, the drums never stop, day or night, for weeks.
Eventually the scientist asks one of the natives about this, and the native's only reply is "Drums never stop. Very BAD if drums stop."
The scientist asks "Why? What happens when the drums stop?"
"Bass Solo."