In one story, Thor encounters the giant king Útgarða-Loki and has to perform deeds for him, one of which is a challenge of Thor's strength. Útgarða-Loki goads Thor into lifting the serpent disguised by magic in the form of a magic colossal cat. Thor grabs the cat around the middle of its belly but is unable to lift such a monstrous creature as Jörmungandr. He manages to raise the cat high enough for only one of its paws to lift from off the floor. Útgarða-Loki expresses how the result was expected and later explains his deception. He acknowledges Thor's lifting of the cat as an impressive deed as he stretched the serpent to where it almost reached the sky. Many watching became fearful when they saw one paw lift off the ground. If Thor had managed to lift the cat completely from the ground, he would have altered the boundaries of the universe.
Thor's fishing trip
Jörmungandr and Thor meet again when Thor goes fishing with the giant Hymir. When Hymir refuses to provide Thor with bait, Thor strikes the head off Hymir's largest ox to use as his bait. They row to a point where Hymir often sat and caught flat fish and where he drew up two whales. Thor demands to go further out to sea and does so despite Hymir's protest. Thor then prepares a strong line and a large hook and baits it with the ox head, which Jörmungandr bites. Thor pulls the serpent from the water, and the two face one another, Jörmungandr dribbling poison and blood. Hymir goes pale with fear. As Thor grabs his hammer to kill the serpent, the giant cuts the line leaving the serpent to sink beneath the waves and returns to its original position encircling the earth. In earlier Scandinavian versions of the myth, Thor successfully captures and kills the serpent by striking it on the head. This encounter with Thor shows to have been one of the most popular motifs in Norse art. Four picture stones that have been believed to have been linked with the myth are the Altuna Runestone, Ardre VIII image stone, the Hørdum stone, and the Gosforth Cross. A stone slab that may be a portion of a second cross at Gosforth also shows a scene of a man fishing for a serpent-like creature using an ox head. These stones did not agree on the myth's conclusion as some had displayed scenes of the serpent escaping by the giant and some of its death. The Ardre VIII stone depicts a man entering a house where an ox is standing, and another scene showing two men using a spear to fish. The image on this stone is dated to the 8th or 9th century. If the stone was correctly interpreted as a depiction of this myth, it would demonstrate that the same of a similar version of the myth remained unchanging for a period of about 500 years prior to the recording of the version in the Prose Edda around the year 1220.
One sign for the coming of Ragnarök is the violent unrest of the sea as Jörmungandr releases its tail from its mouth and thrashes its way onto land. Fenrir will set ablaze one half of the world with fire while Jörmungandr sprays poison to fill the skies and seas of the other half. Fenrir and Jörmungandr will then join the sons of Muspell into the plain of Vigrid. Here is where the last meeting between the serpent and Thor is predicted to occur. Thor will become occupied with battling the serpent and is unable to help others as they fight their own battles. He will eventually kill Jörmungandr but will fall dead after walking nine paces, having been poisoned by the serpent's deadly venom.
draws a parallel between Jörmungandr's biting of its own tail and the binding of Fenrir, as part of a recurring theme of the bound monster in Norse mythology, where an enemy of the gods is bound but destined to break free at Ragnarok.