Plot hole: It's never explicitly stated or shown that the Thing reproduces with each victim until the movie is nearly over (when Palmer infects Windows). Most viewers figure it out from the context, but it's unclear just when and how the characters themselves have come to this conclusion. This was an inadvertent result of an editing decision and a visual goof: there is a deleted scene in which Blair explains much more directly that the Thing multiplies according to how many victims it takes, and in its place in the final film is a scene containing a computer simulation that director John Carpenter acknowledges was a failed attempt at explaining the organism's life cycle.
Plot hole: We see Jason get his outfit from Harold's clothes line. Yet in Chris's flashback Jason has these same clothes already on.
Suggested correction: I went and looked at both Chris version of Jason and Jason in the recent Part III. The Part III Jason outfit in Chris version has a lot darker clothes. Same style, just darker. That type of clothing is very similar though.
Plot hole: In what appears to be at least an hour or so after curfew is put in effect, Challis goes to a liquor store. Even if he didn't know about the curfew, why would the liquor store still be open?
Plot hole: We learn in the film that Cat People must kill a human in order to return to their human form. However, after becoming a cat at the swimming pool and terrorising Alice, Irena becomes human again without making a kill (the only other person at the closed pool is alive and well at the end of the scene - we know Alice has not imagined the presence of the cat because of her shredded clothes). (01:31:00)