"After that Loki hid himself in Franangr's Foss in the form of
a salmon. There the Aesir caught him. He was bound with the guts
of his son Nari, but his son Narfi was changed into a wolf. Skadi
took a poisonous snake and fastened it up over Loki's face, and the
poison dropped down. Sigyn, Loki's wife, sat there and held a cup
under the poison. But when it was full she poured the poison away,
and meanwhile poison dropped on Loki, and he struggled so hard that
all the earth shook; those are called earthquakes now."

_Völuspa_ inserts lines corresponding to this passage after the
Baldr episode, and Snorri makes it a consequence of Loki's share in
that event.

He is more especially agent of the doom through his children:
at Ragnarök, Fenri the Wolf, bound long before by Tyr's help,
will be freed, and swallow the sun (_Vafthrudnismal_) and Odin
(_Vafthrudnismal_ and _Völuspa_); and Jörmungandr, the Giant-Snake,
will rise from the sea where he lies curled round the world, to slay
and be slain by Thor. The dragon's writhing in the waves is one
of the tokens to herald Ragnarök, and his battle with Thor is the
fiercest combat of that day. Only _Völuspa_ of our poems gives any
account of it: "Then comes the glorious son of Hlodyn, Odin's son
goes to meet the serpent; Midgard's guardian slays him in his rage,
but scarcely can Earth's son reel back nine feet from the dragon."

When Thor goes fishing with the giant Hymi, he terrifies his companion
by dragging the snake's head out of the sea, but he does not slay it;
it must wait there till Ragnarök:

"The protector of men, the only slayer of the Serpent, baited his hook