Accompanied by his trusty guide, he too seeks out a very remote locale for researching the mating behaviour of the giant rat of Sumatra. Around dusk of the first day, he's sitting by the campfire with his guide when in the distance, he hears tribal drums. They get louder. The dusk turns evening. The drums get louder.
Evening turns to dead of night.
The drums get louder and louder, until it is obvious that the drummers must be quite close. ON.CA Attribute the joke's source if at all possible. I will reply, mailers willing.