The serpent as impounder of water: in both, the serpent takes the waters into its own keeping (encompassed under Vritra's bulk / swallowed into the Bakhu serpent's body), the world's motion stalls (the rivers penned like cattle / the solar barque standing still), and an armed god compels restitution — the waters are given back in full and flow resumes. Neither serpent consumes what it holds; the Egyptian text even makes the seizure begin with a lowered gaze at Ra — an inspection that becomes an impoundment.
'The Dragon lies beneath the feet of torrents which Vritra with his greatness had encompassed... Guarded by Ahi... the waters stayed like kine held by the robber' — until Indra's bolt 'opened the cave wherein the floods had been imprisoned' and they run 'like lowing kine' to the ocean (vv. 2, 8, 11).
The serpent on the Hill of Bakhu, at close of day, 'turneth down his eyes to Ra; for there cometh a standing still in the Bark, and a deep slumber within the ship. And now he swalloweth three cubits of the Great Water' — until Sutu, with steel, forces him 'to vomit all that he hath swallowed,' and 'the Bark sails on.'
Griffith's vv. 8 and 11 and Renouf's ch. CVIII verified verbatim in the cited scans; the swallow-then-forced-vomit and the penned-kine images are the texts' own words, not paraphrase.
Our fact-checkers corrected the first draft:
The protective coil timed exactly to darkness: a serpent wraps the luminous, meditating/dead-but-living figure for the whole duration of the dark passage · seven days of storm, twelve hours of night · encircling without constricting, and releases the moment light returns.
Encirclement as the serpent's resting posture: neither text has the serpent attack · Jormungandr simply lies around all the earth in the surrounding sea, mouth closed on his own tail; Ahi lies 'couched around the waters,' holding the goddesses 'encompassed.' In both, the coil is a form of custody · the serpent holds a whole category of the world (the dry earth, the celestial waters) enclosed within its ring, keeping rather than devouring, and the enclosure persists until an outside force (Ragnarok, the bolt) breaks it.
In both, heaven never announces the flood openly.
In both traditions repopulation after the flood is not biological but liturgical: the survivor's post-landing sacrifice is the literal manufacturing step for the next humanity.