At the end of the day, the drumming is still going and is starting to get on his nerves. So, he asks another native when the drumming will stop. The native looks as if he's just been reminded of something very unpleasant. "Very bad when the drumming stops," he says, and hurries off.
After a couple of days with little sleep, our traveller is finally fed up, grabs the nearest native, slams him up against a tree, and shouts "What happens when the drumming stops?!!"