Why do infants the world over begin their vocal lives with growls, grunts, squeals, and creaky phonation? And why does this pattern hold across radically different languages and caregiving environments? We propose that the mechanical geometry of the vocal tract at each developmental stage acts as a continuously changing constraint on what infant vocal exploration can discover. Beyond limiting what sounds are possible, this geometry actively generates certain acoustic events as the natural consequence of ordinary exploratory activity. In the neonatal larynx, tissue properties lower the thresholds for phonatory regime transitions; in the tongue, fibre geometry confines early exploration to a single axis until hyoid descent and palatal deepening open new dimensions; in the anterior articulators, independently available components, such as lip closure and jaw oscillation, await the reorientation of suprahyoid muscles that makes their coupling discoverable. Drawing on the motor development literature and neuropsychology of learning, we argue that vocal repertoire emerges through the same discover-stabilise-differentiate logic that governs early limb control: the body generates variation before any intent exists, sensory consequences draw the infant back to the patterns that produced them, and stabilised motor-auditory mappings gradually become communicative resources. The sequence of vocal development can thus be understood as the natural output of exploration within a continuously reorganising anatomy, where each new configuration, through its own mechanical properties, redefines the acoustic possibilities that undirected exploration will discover.