White-water rafting on the Zambesi.
Seeing it happen to someone else merely increases the thud-rate of an already overworked heart, and only when we ourselves fly down the rapid, fling ourselves forwards on Alex's command 'Go!' and experience the exhilaration of total immersion do I begin to relax and even to suspect that I might enjoy myself.
Rapid five is the most spectacular, with a steep drop of more than twenty-five feet. Exhilaration and excitement make up for fatigue as we progress into some longer but less steep runs. I suppose the maximum time we spend on a rapid is no more than forty-five seconds, but into that time is packed an enormous amount of action, and the outpouring of nervous energy can only be released by bawling one's lungs out.
The sheer relief at reaching the tenth and last rapid, with the day's filming done and soft evening light catching the walls of the canyon, leads me to do a Very Silly Thing.
The crew of my raft manage to persuade me that there is an even more wonderful experience than white-water rafting and that is to swim, or rather let your body be carried, down a rapid. I ask about the crocodiles we'd seen further up the gorge. No problem, they avoid moving water. I ask about the rocks. No problem, way below the surface. Such is their enthusiasm and my joy at having survived this far that I surrender to a dangerous streak of natural impulsiveness, and jump, with them, off the raft and into the waters of rapid number ten.