Śivasaṃhitā 3.87

The tongue directed upward (rasanāmūrdhvagā) in siddhasana creates the complete circuit: the heels’ support at the lower cakras impulses prāṇa upward; the tongue in khecarī captures it in its ascent and directs it toward the skull’s soma maṇḍala. The lunar fluid (candre salilaṃ) that the yogin «drinks» is the amṛta flowing from the coronary center toward the more subtle tissues of the superior nervous system.

That siddhasana is «the most secret posture in the world» (nāsti gopyataraṃ loke) does not allude to its technical difficulty but to its spiritual efficacy. The secret in tantric tradition is not what is hidden by caprice but what requires adequate preparation to be received without harm. Siddhasana practiced prematurely without prior nāḍī purification can produce prāṇa disturbances instead of liberating it.

Liberation from sin (pāpamuktā) through contemplation in siddhasana operates differently from other chapter techniques: not through prāṇāyāma’s fire but through direct contact with amṛta that dissolves karma as water dissolves salt. It is a softer path of dissolution than combustion, though equally effective at the level of deep transmutation.