摘要
最近，我在南非克鲁格尔国家公园看见一条沿道路形成的湿线，歪歪扭扭但可以明显看出某种复杂却有周期的图案。我的向导也是动物学专家，告诉我那是发情期公象留下的尿迹。公象到了这种非常时期（也许是南半球动物区系类似大象的动物在“远足”的时候），会不同程度地持续尿遗失禁，显然是为了留下味迹。这条沿路两边摆动的尿迹波形曲线可能是长长的阴茎随大象四足踩着笨重的脚步周而复始却不规律地移动而摇摆形成的（事实上阴茎不是地道的牛顿摆；假若如此，这条曲线应是正弦波）。
I recently saw, on a road in the Kruger National Park in South Africa, a wiggly wet line which followed the course of the road and apparently traced out some kind of complicated repeat pattern. My host and expert guide told me that it was a trail of urine from a male elephant in musth. When a bull elephant enters this curious state （perhaps the elephantine equivalent of an Australian on ＂walkabout＂） he dribbles out urine more or less continuously, apparently for scentmarking purposes. The side-to-side waving of the urine trail on the road was presumably produced by the long penis acting as a pendulum （it would be a sine wave if the penis were a perfect, Newtonian pendulum, which it is not） interacting with the more complicated periodicity of the lumbering four-footed gait of the whole animal.
