The size and shape of this vessel indicate that it may have been a Cham-Mwana changdu used to divine illnesses. The lip plug is of the type once worn by local women.
General information about Vessels Transferring Disease:
Across the Western Gongola Valley, healing vessels were commonly used in ritual procedures enacted by healer-diviners to transfer the spirits of disease from a patient to a specially made ceramic pot. Typically, a piece of wet clay was circled around the patient’s body to help coax the disease into the clay. The healer-diviner then incorporated the clay into a newly modeled pot, whose features sometimes described the physical symptoms of the illness itself. Firing the pot—and transforming it into ceramic—helped secure the transfer of the disease.
Source: Gallery Wall Text, Central Nigeria Unmasked: Arts of the Benue River Valley, 2011