After Norris suffers an apparent heart attack, the men rush him to the medical ward, where Copper attempts to re-start Norris' heart by defibrillation. The electrical shock, however, causes the Norris-Thing to transform and defend itself. This revelation was hardly in the Thing's interest. Having copied Norris' body exactly, including the defective heart, it apparently suffered a genuine heart attack and possibly had its consciousness degraded to the point where it reacted instinctively rather than intelligently against the electrical shock. If it retained human-level intelligence, it would have known that the shock was not actually an attack with hostile intentions. (By an alternative interpretation, Norris was taken over gradually after a limited, perhaps one-cell infection, and did feel strange; this would be why he earlier refused leadership and said he did not feel up to it. If so, the Thing may not have reached the point where it actually took over his mind and gained access to his human knowledge.)
Changing its ribcage into an enormous vertical maw, lined with razor-sharp teeth, the Thing bites off Copper's hands; he quickly dies of blood loss. It then begins to mutate even further, as a serpentine/spider-like creature explodes from the chest cavity. Its head is approximately human, but it is like a grotesque parody of Norris' features, with sharp, fang-like teeth.
As it roars at MacReady, clinging to the ceiling, Macready advances toward the creature and sets both the snake-spider Thing and its torso on fire with his flamethrower. While the men panic and its body burns, the Norris-Thing's (original) head tears away from its burning body and grows spider legs and pair of bug eyes. It hides under a nearby table and then attempts to scuttle off, only to be spotted by Palmer and Windows. (Palmer, himself a Thing at this point, apparently tried to divert suspicion from himself by making an incredulous exclamation at the sight of the spider-head. It may be noted that he only speaks out once Windows has also seen it and its survival is compromised anyway.)
MacReady turns and incinerates it as it attempts to escape through the infirmary room door. Noticing how every part of the Norris-Thing had an instinctive desire to survive, MacReady developed a heat-based blood test for testing the remaining men.
The Norris-Thing is shown to possess a minimum of three distinct forms: