When Frigg collected oaths from all creation not to harm her son, she passed over one plant growing west of Valhalla — the mistletoe, too young, she judged, to swear. Loki, in disguise, teased that one exemption out of her, cut the sprig, and put it in blind Höðr's hand at the weapon-throwing game. The softest thing in the world killed the brightest: the myths understand that doom enters through the clause everyone thought too small to matter.
Among the artifacts of the North, Mistilteinn is the anomaly: not forged by dwarves, not owned by a god, no gold hilt, no name-day in a smithy. It is a twig — and it did what no blade or hammer in the nine worlds could do. In the catalogue of things that changed the fate of the gods, it sits beside Mjölnir and Gungnir, weightless.
The death of Baldr
Baldr the bright, best-loved of the Æsir, began to dream of his own death, and the gods took the dreams seriously. Frigg travelled creation extracting oaths: fire and water swore, iron and every metal, stones, earth, trees, sicknesses, beasts, birds, and serpents. The oaths held so well that Baldr's invulnerability became the entertainment of the gods' assembly: he stood in the ring while the Æsir shot at him, hewed at him, and pelted him with stones, and everything fell harmless. It is the happiest scene in the mythology, and it is built directly over the trapdoor.
Loki, displeased that nothing harmed Baldr, took the shape of a woman and called on Frigg at Fensalir, asking in idle-seeming talk whether truly all things had sworn. All things, Frigg said — except one small shoot growing west of Valhalla, called mistilteinn, too young to demand an oath from. That was everything Loki needed. He pulled up the sprig and carried it to the assembly, where Höðr, Baldr's blind brother, stood at the edge of the ring, empty-handed. Why not honour Baldr like the others, Loki asked. Höðr answered with the facts: he could not see where Baldr stood, and he had no weapon. Loki gave him the mistletoe and guided his aim. The shaft went through Baldr, and he fell dead to the earth. Gylfaginning calls it the greatest misfortune ever among gods and men — and the gods could not even take vengeance on the spot, for the place was so holy a sanctuary that they could only stand and weep.
What followed is its own cycle of stories: Baldr burned on the ship Hringhorni with the ring Draupnir on the pyre; Hermóðr rode to Hel, whose bargain was that Baldr would return if all things wept for him; and the giantess Þökk — Loki again, the sources say — sat dry-eyed in her cave so the dead stayed dead. Vengeance came twice: Váli, born and grown in a single day, killed Höðr, and the gods ran Loki to ground and bound him. One overlooked twig, and the whole mythology tilts toward Ragnarök.
Why did mistletoe kill Baldr?
Within the story, because of a loophole: too young to swear, therefore never sworn, therefore the one free agent in a universe under oath. But the choice of plant is not arbitrary. Mistletoe grows rootless in the boughs of other trees, suspended between earth and sky; neither properly tree nor herb; green in the dead of winter. It slips every category the way Loki slips every oath — the perfect weapon against a system of total classification, because it was never really in the system. Völuspá's seeress dwells on the wrongness: the mistletoe stood slender and most fair, grown higher than the plain, and from that slim shoot came the deadly dart that Höðr hurled.
The sources do not tell it identically. Snorri's Gylfaginning gives the full plot with Loki as engineer. Völuspá, far older, names the mistletoe and Höðr as the shooter but never shows Loki guiding the blind god's hand — though it moves straight on to Loki bound in punishment, so the connection is old. And Saxo Grammaticus, in his Latin Gesta Danorum, changes almost everything: his Høtherus is not blind, not a dupe, but a warrior rival who kills Balderus with a special sword; the mistletoe is gone entirely. The twig belongs to the Icelandic tradition — the one the world remembers.
The sword called Mistilteinn
Norse legend was unwilling to let the name retire. In Hrómundar saga Gripssonar, a late legendary saga, the hero Hrómundr breaks into the barrow of the draugr Þráinn and takes from him a famous sword named Mistilteinn — the murder weapon reincarnated as heirloom steel. A different object in a different story, but the borrowing shows what mistletoe had come to mean: the thing that kills what cannot be killed.
At Ragnarök
The mistletoe's work is the one wound Ragnarök heals. Both Völuspá and Gylfaginning promise that in the renewed world after the fire, Baldr comes back from the dead — and Höðr with him, the thrower and the thrown reconciled, dwelling together where fields grow unsown. The murder that all creation's weeping could not undo is undone by the end of the world itself: the twig cut west of Valhalla is only finally answered in the green morning after.
Is kissing under the mistletoe from Norse mythology?
Not in any source we have. A much-repeated modern retelling finishes the myth sweetly: Frigg declares the mistletoe a plant of love, her tears become its white berries, and all who pass beneath it must kiss. None of that appears in the Poetic Edda, the Prose Edda, or Saxo. The kissing custom is documented from eighteenth-century England; the link back to Frigg is a later back-formation — charming, but a modern story about an old story. What the ancient world did attest is mistletoe's strange sanctity: Pliny the Elder describes druids cutting it from oaks with golden sickles. The plant was numinous across old Europe; the Norse gave its uncanniness the darkest job.
In the primary sources
Gylfaginning in the Prose Edda carries the full narrative: Baldr's dreams, Frigg's oaths, Loki's interview at Fensalir, the sprig west of Valhalla, and Höðr's guided throw. Völuspá in the Poetic Edda is the oldest witness, giving the mistletoe, the fatal shaft, Höðr as slayer, and Váli's vengeance in a few compressed stanzas. The Eddic poem Baldrs draumar has Odin ride to Hel's gate to learn Baldr's fate and hear that Höðr will be the bane — though it never names the weapon. Saxo's Gesta Danorum preserves the divergent Danish tradition without the mistletoe, and Hrómundar saga Gripssonar contributes the barrow-sword that inherited the name.
Legacy
Mistletoe may be the only murder weapon in world mythology that people now hang over doorways in December. Its modern career runs almost perfectly opposite to its mythic one, and the irony has kept the Baldr story alive in every retelling. It remains the purest expression of a Norse idea: fate does not force the locked door; it walks through the one nobody thought to lock.
Frequently asked questions
Was the mistletoe an arrow, a spear, or a dart?
The sources are loose about it. Snorri has Loki hand Höðr the sprig to throw; Völuspá calls it a shaft or dart that Höðr shot. Saxo, telling a different version, arms his Høtherus with a sword instead. What matters in every telling is the material, not the form: it was mistletoe, the one thing unsworn.
Did Loki kill Baldr?
By proxy. Höðr's hand threw the sprig, but Loki found the loophole, cut the twig, armed the blind god, and aimed him — then, as the giantess Þökk, refused the weeping that would have brought Baldr back. The gods judged him the author of it: his capture and binding follow directly from Baldr's death.
Why didn't Frigg make the mistletoe swear?
Gylfaginning says she thought it too young — too slight and green to demand an oath from. The myth's cold lesson is that the exemption, not the enemy, is the danger; the one thing excused from the system is the one thing that can break it.