The corderi /kɔrˈderɪ/ is a dark brown stranger characterized by its hard, ribbed skin, indented eye markings, and sharply curved claws. The corderi's arms, legs, and tail tip lack ribbing, and are covered, instead, with a soft, thin skin.

Although the strain's grey, slimy flesh radiates heat, the ribbed sections of its body act as insulation, and thus, only the corderi's arms, legs, and tail tip are warm to the touch. The rest of its surface is plasticine, and sounds hollow when tapped, with 0.07% of individuals producing a second tapping sound one to two seconds after being tapped or struck.

Its mouth contains small, evenly spaced teeth, and a short tongue which ranges in color from soft grey to a healthy pink, a hue shared by its gums. Its jaws tends to remain in a fixed, slightly open position, and its oral cavity leads nowhere. Though the stranger has no particular odor of its own, its body tends to absorb^ȸ the scent of its surroundings.

The corderi does not respirate, but seems to require oxygen to survive, and drowns instantly when its mouth is submerged in water. Fire, meanwhile, causes its arms and legs to melt, and its ribbing to grow brittle and crumble apart. The strain is similarly vulnerable to extreme heat and cold, and dies via violent seizure in temperatures above 126°F or below -5°F. Its weak flesh takes several months to heal from even small cuts, and with significant scarring afterward; thankfully, the corderi is protected by its ribbed segments, which are difficult to pierce or bend, though exhibiting the accumulation of natural wear and tear over the course of the stranger's life.

The corderi speaks in nonsensical human speech, with a moderate-to-severe stammer depending on the individual. Its voice is always raspy and quiet, and is deep in tone 94% of the time, with the remaining 6% of individuals presenting with a more medium-pitched, or child-like voice.

When it first appears, the corderi grows from a small, fetus-like form, which starts off smooth and pale in coloration. Its pigment darkens as it develops, with the strain's characteristic ribbing appearing towards the end of its growth. Once development is complete, the corderi uncurls and stands up, grooming itself fastidiously to remove any dirt which may have accumulated on its skin during formation, then scurries off into the shadows. Groups usually appear in small piles, which awaken in unison and scatter in separate directions.

Rarely, individuals appear inside small cavities beneath floors or inside walls, and die once they grow larger than the space allows. Any fully developed corderi always scratches at the wall or floor around a trapped individual in an attempt to free it, and stops only when the trapped corderi either dies, or is liberated from its confinement.

The corderi possesses a skittish disposition. It is wary of changes, and avoids all loud sounds, bright lights as it moves through its environment in consistent, looping paths. It tends to dig, and is adept at hiding the entrances of the passageways that it constructs. Although it does not swim, it can navigate through passageways filled partially with water by laying on its back or side (its mouth at least half-exposed to air), and pulling itself forward with its claws on the ceiling.

At shallow depths, the corderi's tunnels are twisting and chaotic, with maze-like junctions and dead ends. As it burrows deeper, however, these tunnels become straighter, with 90° turns and long corridors that correspond with latitudinal and longitudinal lines.

The corderi displays some hoarding behaviours towards small, random objects, and carries them in its mouth as it travels along its path. At some point, it will find a spot in the walls that catches its "interest", at which point the strangers embeds the object in the dirt. Objects tend to be placed in clusters, and in a heavily infested area, a single tunnel may contain hundreds of objects placed there by dozens of individuals, their arrangements^ჟ forming intricate, mural-like designs.

Although the corderi is not violent towards others of its strain, it does display occasional coarseness towards those nearby. It is not uncommon for the stranger to roughly push or growl at an unfamiliar individual of its strain – the corderi at the receiving end of this aggression, however, does not react to this incivility, continues on, unperturbed. Otherwise, interactions between corderi tend to be brief, and consist of short "conversations" of tapping/stroking motions to the mouth and side of the face.

All objects generate in a slow and organic matter. A pen, for example, starts off as a small plastic nib, and grows larger and more complex over time, as though it were a developing embryo, while a book blossoms outward from a clump of crumpled paper.^Ͽ

This duplication appears both harmless and involuntary, and the corderi itself makes no indication that it is even aware of this process. Each corderi duplicates within its inner tissues between one and seven objects over the course of its life, and these objects do not distort its form or impede its life in any way.

The corderi sometimes creates a duplicate of another corderi's imitation object, and thus, deformities continue to propagate and exaggerate. Over a long enough timespan, generated objects grow more and more meaningless and abstract, until the corderi generates curved, nondescript shapes, bulging plastic ruffles, and flat polygons which bear no resemblance to the original object.

The corderi watches sensitives from a distance, and with nervous suspicion, running away when approached. It always chooses flight over fight, and, when attacked, grows agitated and spasmic, rather than defensive and violent. Further, it tends to abandon^Ꮵ any territory into which a sensitive repeatedly ventures.

The corderi sympathetically picks up nervous tics^Ⴢ from the sensitives it meets, even when these tics are not apparent during the encounter itself. These tics can even become injurious in the case of skin-picking or teeth grinding, but otherwise, tend to only mildly inconvenience the strain. In addition, strongly afflicted corderi seem capable of spreading these tics to others, and populations can eventually become overrun by these neurotic and often injurious actions.

At the end of its life, the corderi's nervous tics become more pronounced, and its movements, less and less co-ordinated, in turn. A dying corderi seeks out a quiet, secluded place; there, it groans and wheezes, traces its fingers along the grooves between its ribbed stripes, tilts its head to place small pebbles, grit, or pieces of garbage inside its indented eye markings, and taps its teeth one-by-one, as though counting them.^ћ Its companions give it a wide berth during these final days, until the stranger dies with a shuddering rattle.

A dead corderi's eye markings lose their indentations in an instant, leaving behind a flat surface with no crease. The inner flesh begins to rot and break apart within the next few days, while the ribbed sections separate, and grow brittle. Other corderi hoard any objects left behind, but display no other interest in the corpse, which decomposes fully within several months.