Notes on Jörmungandr and the fishing trip
Jörmungandr is the middle child of Loki and the giantess Angrboda, thrown into the sea that surrounds the world. It grows until it circles the world entirely and can bite its own tail, which is where the more familiar image comes from.
The episode everyone remembers is Thor going fishing with the giant Hymir and hooking the serpent instead of a fish. What is interesting is that the surviving accounts do not agree on how it ends.
In one telling Thor hauls the serpent up and is about to strike when the frightened giant cuts the line, and the creature sinks back. In another Thor does strike, and the question of whether the blow killed it is left carefully open. A third version, preserved only in fragments of skaldic verse, seems to assume the serpent died there — which is awkward, because it has to appear again at the end of the world.
It is tempting to pick the version that makes the best story and treat the others as corruptions. But the variation is itself the evidence: these were told aloud for a long time before anyone wrote them down, and the written versions are late, Christian, and working from material their authors did not fully believe in.
Snorri in particular is writing a handbook for poets, not a scripture. He needs the stories to be coherent enough to use as reference. Where his sources conflict, he chooses, and he does not always tell you that he chose.