Fellfang Wurm

A huge, burrowing carnivore native to dry plains areas, the Fellfang wurm is best known for the unusual strategy employed to defeat it. Though it has a tough, armored outer hide, its interior is soft and affords little protection and its teeth are underdeveloped, having evolved to primarily consume small game. When a wurm is hungry enough, it will attack humanoids, and its habit of leaping from the ground and ramming opponents with its body can prove deadly. Paradoxically, playing dead and allowing yourself to be consumed is often the best strategy against the creature. The soft interior of its mouth and proximity to its brain means that if a swallowed creature is tough enough and has a sufficiently small weapon, they can do far more damage in the creature's mouth than from outside it.
Of course, the inside of its mouth is hardly safe, and creatures have to survive the grinding teeth and the muscular sheath that will try to force them further down the wurm's gullet into the acid of its stomach. Some wrackland tribes consider killing a wurm this way to be a right of passage, though only the most brutal of them expect the deed from anything less than a seasoned warrior.
The infamous and reckless nature of this tactic has led the Fellfang wurm to become a popular metaphor in the Federated city-states, referring to a bad situation that must be embraced head-on rather than avoided. A typical sentence might run "yeah, asking where he got the money would make him angry, but we have to know. It's a bit of a Fellfang's Maw."
The creatures hunt by sensing tremors in the ground, and while they usually stick to smaller game, particularly large, aggressive or desperate specimens will attack almost anything that moves. They usually claim a certain area as territory and hunt there exclusively, but in times of famine huge numbers of the beasts may be driven from their habitats to seek better stocked pastures. These large-scale migrations often become infamous natural disasters, with the influx of wurms and casualties in combating them becoming war stories told for generations in the localities unlucky enough to be in the path of a migration.