If the adventurers are smart, they can solve this riddle and get the information they need.
To be used for the final encounter, find the final treasure, or anything that needs to be hidden away better then normal. Typical “who the heck would ever spend the time making it” but it is fun and a mental challenge for a change.
Then suddenly all your body paralizes and you hear a voice echoing in the distance "seems like another rat has been lured to my maze," this voice was terribly cold but playfull, "come on you are not already planning on leaving, the fun has only begun."
Swordbiters are parasites. They are long, thin and silver, and digest metal, somewhat like rust monsters, but smaller and more insidious. They resemble stick insects, but when they cling to metal they are very well camouflaged, and one can be biting your sword for a week before you notice it. They cannot be removed by hand, as they are very strong, but if the blade is inserted into fire they will leap off to escape the flames. Sometimes, old treasure hoards are infested with them, and the first glimpse you get of the "glittering" weapons is a pile of rusted swords encrusted with these thin silvery insects.