"The difficulties of interpretation were pointed out by Yāska in his Nirukta nearly 3,000 years ago: Sanskrit: tat ko vṛtraḥ?—meghaḥ iti nairuktāḥ, tvāṣṭro ‘suraḥ ity aitihāsikāḥ (Nirukta 2.16) English: “That (who) Vṛtra?”—“A cloud” says the narrator, “An asura, Tvaṣṭri’s [son]” say the story-tellers."