system
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human
[John Carpenter's The Thing] So was Thing a creature or a virus? (possible spoilers?)

Maybe I missed something but in the movie it seems like the crew killed The Thing multiple times with fire and yet there seemed to always be another one? So does The Thing make a copy of itself when it finds another host?
gpt
It was a pathogen, most likely transmitted by skin-to-skin contact. It would eat the host's cells one by one, and turn itself into copies of those cells that mimicked the host's. When stressed, it often would shapeshift into "remembered" shapes from previous hosts to defend itself. This is why the blood test worked, and it probably would only produce a positive result if the host was in the late stages of infection. 

The most effective thing about this mode of infection was that a person could be infected while retaining their mental functions, as the Thing thought their thoughts by mimicking their nervous system. They could be completely unaware of what was lurking inside them, and even as their body changed they might retain awareness (to their shock and horror, of course). The entire research team was probably infected early on.