Once upon a time, animal dung -- and crocodile dung in particular -- was considered to have special powers. This belief was especially popular among ancient Egyptian and Indian women. Part of its mysticism was its alleged ability to prevent conception, and women mixed it with honey (and maybe some sodium carbonate) and inserted the resulting ball as a vaginal pessary.
It may not have been superstition -- or, frankly, the odor -- surrounding the pessary that was an effective way to prevent pregnancy. As it turns out, dung has a high level of acidity, and its alkaline properties may have given it some effectiveness as a spermicide. The placement of the dung may have blocked some sperm from reaching their ultimate destination as well.