Magnet smoolks use aligned nodes of magnetite in their bodies to orient themselves and avoid tunnels that are too high in oxygen.
Magnet smoolks form complicated magnetite-seeking networks that are similar to plant roots seeking water. When a growing magnet smoolk finds a deposit of magnetite, it turns into a "node" and reproduces. A cloned bud forms on one side and becomes a "string." Like a root cap, the string's tip is coated in mucilage to ease passage through soil. Unlike a root cap, the tip also has an protein-digesting enzyme called bromelain. The bromelain works like a machete in that it can be used to clear the way and attack other magnet smoolks. The bromelain itself is colorless; the mucilage it is carried in is yellow.
If a magnet smoolk string is unable to find magnetite soon enough, its starvation triggers a cellular "kill switch". Though the "kill switch" is unfortunate for the starving string, it ultimately benefits the group. After the string's death, a thin goo---its liquefied insides--seeps through the tunnel. The chemicals emitted by the body of a dead string alerts the node to bud in another direction. The seeping goo can also be reabsorbed by the node to help create another string.
The dried, blackened husk of the dead string impedes passage through the occupied tunnel. Magnet smoolks attempting to travel (that is, grow through) tunnel use their bromelain machetes to dissolve the husks.
If a magnet smoolk has accessed a large magnetite deposit, it will block several tunnels by swelling the tips of strings in those tunnels. The swollen string tip acts as a roadblock to other magnet smoolks, forcing them to make their own tunnels to go around the obstacle. (which they prefer not to do) In the right conditions, the string may use its "machete" to hack through the roadblock. One of the conditions that causes this behavior is extreme hunger. In extreme hunger, they run out of magnetite, cannot dig well, and are unable to avoid oxygen traps. In such occasions it is prudent to follow a preexisting path into a safe and food-rich area.