Śivasaṃhitā 3.70

Eight daṇḍas (each daṇḍa equals twenty-four minutes: eight daṇḍas are exactly three hours) of vāyu niścala — completely motionless air — for the yogin. Not forced breath retention but the spontaneous cessation of respiratory movement: the body, saturated with prāṇa, no longer needs ordinary gas exchange. This is kevala kumbhaka, the effortless retention that the Haṭhapradīpikā describes as the highest sign of advancement.

The technique of «drinking air in the form of a crow’s beak» (kākacañcvā) is a prāṇāyāma variant using the mouth pursed in the form of a crow’s beak to ingest cold air in a controlled manner. The coldness of the ingested air contrasts with the heat of internal fire (agni) and produces the digestion of subtle toxins. Śītala (cold, refreshing) is the air quality acting as balm on the nervous system overheated by intense practice.

The «one entitled to liberation» (mokṣabhāgin) — literally, one who has obtained their rightful share of liberation — is a revealing formulation. Liberation is not something obtained instantaneously as a prize but something of which one becomes bhāgin, a legitimate participant. The yogin who has arrived here can no longer fail to be liberated: the mechanics of awakening are irrevocably in motion.