The nails gradually built up over time and each reflects an invocation. Nkisi figures can be either human or animal and were believed to have the power to hunt down wrong-doers. This nkisi figure is the double-headed dog Kozo. In Kongo society, dogs were seen as particularly good at hunting down wrong-doers as they were mediators between the seen and unseen, the living and the dead. They could therefore move easily between the known and unknown to hunt down their pray. Kozo's two heads and four eyes made him particularly good at seeking out invisible causes.