Were-Jackals of the Congo

In the 1930's perched hidden in a tree an English physician witnessed a very special ceremony. It started with the  beating of drums, then the nyanga (witch doctor), covered in the skin of a jackal, jumped into the center of the crowd and began to chant.  The chanting grew louder, and the energy of the crowd grew as well.  In the middle of the circle, the nyanga prepared a potion, and, as the silence came to a halt, he drank the potion, and unleashed the cry of a jackal.  The nyanga worked himself into a frenzy beyond his physical ability, and then fell into a trance.  During the trance, a man and woman jumped into the circle, and preformed a dance which became increasingly animal like as it progressed.  Then, in an instant the two turned into jackals before the physician's very eyes.