Factual error: It's supposed to be late autumn, but in most scenes the leaves are still very green. [This is because it was shot in California during the summer. Carpenter imported leaves for every shot that you saw leaves blowing on the ground and blew them with a giant fan (this also killed any ambient sound takes); there are also a few shots where you can see palm trees (most prominent the one right in the front yard of Michael Myers' house).]
Factual error: In the scene when Laurie gets stabbed by Michael in the arm she falls over the banister - the camera shows a view of what she sees, falling at that angle Laurie would have broken her neck, spine and hip. But it is still weird how she managed to turn 180 degrees in such a short fall.