Prior to the widespread adoption of Christianity in the early twentieth century, magic formed an important element in Batak religious practice. Religious specialists, known as "datu," performed both benign and malevolent magic using a variety of ritual paraphernalia. The most sacred and powerful of the datu's objects was the potion container, or "guri guri." These containers held "puk puk," a powerful substance made from a ritually executed human victim. Puk puk, it was believed, could force the victim's spirit to do the datu's bidding.The containers themselves were often imported Chinese ceramics, but the Batak carved elaborate wooden stoppers to seal the mouths of the vessels. Many stoppers, such as this example, depict human figures riding horselike creatures called "singa." Combining aspects of horses, snakes, lions, and other animals, singa are mythical creatures associated with fertility and supernatural protection.