Sealed with Bright Runes

I know a charm:
it will save me if Malice
cuts dark runes on a sapling’s roots
with intent to harm;
it turns the spell;
the hater is harmed, not me.
Ponderous with plots,
the Wobble-Troll defeats
herself into nowhere: airless Niflheim.
Bright runes I know
which trolls know not,
nor might trolls ever mount to mind.
                   —Rígsþula