Among Yorùbá drummers in southwestern Nigeria, the Dùndún drum is described as Òkú Ewúrẹ́ Tó ń F’ọhùn Bí Ẹ̀nìyàn—“the dead goat skin that vocalizes like a human.” This formulation locates vocality within the drum’s membrane rather than in human technique alone. While scholarship on Dùndún richly documents its social functions and speech imitation, it often treats the instrument as acoustically neutral, overlooking how the membrane’s physical behavior conditions vocal expression. This paper argues that Dùndún vocality emerges through the material responsiveness of goat skin under shifting conditions of pressure, tension, heat, and touch. Drawing on four months of performance-based ethnography in Ìlorà, Òyó State, I employ a method I term material tracing: tracking how physical changes in the instrument—such as fluctuations in elasticity—shape performance decisions. Through analysis of archival recordings, Yorùbá proverbs that encode material knowledge, and interviews with master drummers, I demonstrate that the membrane moves through multiple material states that yield distinct vocal registers, including melorhythmic (àlùjó), nasal, ohùn agogo, and speech-surrogate vocality. Drummers actively regulate these states through environmental and tactile interventions, such as applying solar heat to tighten slack skin or binding twine around tension cords to recalibrate response. Vocality thus arises not from inert matter but through dynamic engagement with a responsive membrane. By foregrounding this material encounter, the paper reframes instrumental voice as a relational achievement in which sound, meaning, and agency are co-constituted across human and material bodies.