What you fear most... is among you.
Why it is hard sci-fi
Carpenter shoots a procedural horror about an isolated Antarctic research station infected by an extraterrestrial organism that imitates host cells. The film walks the team through real diagnostics. Blood tests with a hot wire, behavioural tells, and a rationing of the few flamethrowers in the camp. The science is held to one rule. The Thing assimilates by direct cellular contact and propagates from any infected cell.
Science inside it
Extraterrestrial parasitic biology with a per-cell replication rule, Antarctic field research logistics, and the diagnostic problem of telling an infected human from a healthy one when the infection is sub-clinical. The blood test scene is one of the best applied-science set pieces in horror cinema.