Śivasaṃhitā 5.204

Concrete instructions on posture and environment reveal that even the highest yoga requires adequate physical conditions. Svastikāsana stabilizes the body for prolonged practice, and the absence of animals and insects (jantu-varjita) ensures prāṇa is not disturbed by bites or distractions. Preparing physical space is yoga as much as the posture itself.

Svastika = the auspicious sign (su = good, asti = being, ka = diminutive), here the āsana where the feet are inserted between the opposite thighs, sumaṭha = good monastery or hermitage (su = good, maṭha = building for practices), jantu = animal/insect, varjita = avoided/free from. Vidyādharas are mantra masters who move freely through space.

Kāmarūpatā (ability to assume any desired form) is one of the most mentioned siddhis in tantric and Nātha tradition. It is interpreted both literally (physical body transformation) and symbolically (absolute flexibility of consciousness to adopt any perspective). Nāthas like Gorakṣa and Matsyendra are celebrated in hagiographies for their bodily transformations.