Śivasaṃhitā 4.84

The introduction of huṃkāra — the seed sound huṃ — as a technical component of advanced Vajrolī adds a vibrational dimension to the practice. The bījamantra huṃ is the seed sound of Śiva in his fierce form, associated with fire (agni) and with the destruction of ignorance. Its intoning during practice is not decorative but functional: vocal vibration creates a resonance in the subtle body that potentiates the contraction of apāna.

Huṃhuṅkāra is the reduplicated form of huṃkāra (the realization of the sound huṃ), indicating that the sound is repeated rhythmically, creating a sustained vibrational pattern. The combination of muscular contraction (apāna) and sonic vibration (huṃkāra) creates a synergy between the physical (sthūla), energetic (sūkṣma), and causal (kāraṇa) levels of the body, acting simultaneously on all three planes of practice.

The alternative of milk (dugdha) as a substitute for the sexual fluid is a principle of graduated pedagogy: the text offers a level of practice accessible to those who do not work with partners in tantric ritual but wish to obtain the benefits of Vajrolī. Milk is considered in āyurveda ojas-vīrya (generator of ojas), and its conscious absorption during the state of apāna retention can function as a physiological analogue of the complete practice.