The Thing is an extremely hostile shape-shifting extraterrestrial organism and the primary antagonist of the 1982 science-fiction film The Thing, its prequel, video-games and literature. The Thing has the ability to assimilate other life forms in order to survive and spread. The original physical characteristics of The Thing and its motivations are unknown as it could have assimilated hundreds if not thousands of other species before it crashed on Earth.
Unlike most creatures, the Thing possesses no inherent standard anatomy. It may very well be that the Thing is a colonial organism whose assimilation instructions are carried on the genetic level. The Thing's shape-shifting nature means that the biology can be the same as the organism it has replicated, or is in the process of replicating. The Thing has the ability to reconstitute itself following immense damage, and is invulnerable to most conventional forms of attack. However it is vulnerable to fire and potentially molecular acid since they both destroy the creature at a cellular level. It is very tolerant of cold, placing itself in cryogenic stasis until found by unsuspecting victims. When changing form, it bursts open and allows a variety of strange and terrifying forms and bits of previously assimilated anatomy to form, such as: tentacles, insect-like limbs, eyes, teeth, claws, even faces, eventually re-arranging its cellular structure to mimic its desired shape. The Thing is also capable of continuing normal functions even when lacking eyes, ears, sense of smell or other ways of interacting with the environment and is capable of producing said organs/appendages to accomplish those functions.
Spider-Thing, Spider-Thing... Does Whatever a Spider-Thing Does.
In the 2011 prequel film The Thing, American paleontologist Kate Lloyd discovers the creature is unable to mimic non-living/inorganic material such as metals or plastic, when she finds a small pool of blood with metal fillings; surmising the creature spat them out when it assimilated its victim.
Any form of the Thing is capable of frightening amounts of strength, speed and stamina, such as the case with the Kennel Thing, which subdued and assimilated multiple sled dogs, and especially the Centipede-Thing, which overpowered Jonas in moments, despite the vast size difference.
"Did somebody order a plate of butt-ugly?"
The Thing is a shape shifting organism, but it must come into contact with its host in order to begin the process of analyzing and copying its cellular structure. To do this, the cells begin digesting and replicating the host, eventually taking over the entire body. The Thing will also only assimilate freshly killed or still living prey; any organism that has been dead for an extended period of time will be ignored by it. This may be due to it being largely ineffective to more intelligent prey if it mimicked a member of their society that was known to have been killed. Alternatively, it may rely on the blood stream to rapidly assimilate prey. Copper was killed by the Norris-Thing biting off both his hands, and so presumably was exposed to Thing infection; yet his corpse showed no signs of "reviving" as an imitation (and a post-mortem blood test came up negative). Presumably he bled out so quickly that the infection had no time to spread before his biomass was rendered useless by death.
"Damn it, Jed! What did I tell you about drooling all over the new carpet!"
After The Thing has assimilated an organism, it is capable of imitating them exactly down to their memories, characteristics, mannerisms, and all of their traits. Even anatomical anomalies and health defects like Norris' weak heart are replicated. When a part of The Thing becomes cut in two, both of those pieces become their own creatures and operate separately. For example, when the Norris-Thing's head grows legs and attempts to escape. The replication varies depending on the occurrences at hand and whether or not the attacking Thing is smaller or is injured. If the assaulting Thing in question is injured in any way, much smaller than the prey or under pressure, it will usually just add the bio mass to itself and either mimic the prey or add the mass to its original frame to increase its size and strength to counteract any threats within the area. If however the Thing successfully assaults the prey in a safe location, it will just feed on the prey and make a copy of the victim then revert back to its cover before searching for another victim to assimilate.