A very distinctive marking
One very dark night, a mother Waterbuck was grazing near the Tribesman's wooden hut with her young calf. The Tribesman had been very busy that day, painting his hut white, and had left the tin of white paint outside his door ready to continue his work the next morning.
The grass outside the Tribesman's front door was particularly lush, and the mother Waterbuck couldn't resist wandering over and eating it.
Her calf followed her, but unfortunately, because it was so dark, the baby Waterbuck accidentally knocked over the tin of paint, and the noise awoke the Tribesman.
The Tribesman came outside, and saw to his dismay that all his white paint was spilt on the ground. The Waterbuck and her calf quickly ran off, but the Tribesman was so angry he gave chase and threw the empty tin of paint at them.
The tin landed firmly on the mother Waterbuck's hindquarters, and left a large round white mark on her bottom.
However, rather than being upset, she was actually very pleased, as the white mark showed up very well at night and helped her calf to follow more easily.
When all the other Waterbuck saw this, they thought it was a good idea too, and to this day, all Waterbuck, even the males and the young calves, have a white mark on their hindquarters.