Factual error: When they are refuelling the helicopter (as a zombie approaches quietly from behind) the actor has put the gas nozzle not into the hole for the gas tank, but into one of the foot-holes that helicopter mechanics use to climb up to the top of the helicopter to do repairs. It doesn't even fit properly. (00:22:55)
Visible crew/equipment: You can see a crewmember in the woods, when Jennifer throws the huge log at the guys, during the big chase scene. (00:05:20)
Revealing mistake: When the father and son climb out of the chairlift and hold on for their lives, the kid is very obviously replaced with a grown-up stunt.
Visible crew/equipment: In the scene near the start of the movie when Lois Chiles is showing Mia Farrow her bathroom and Mia Farrow is saying "Yes, It's lovely," on the mirror on the right you can see a member of the crew crawling around on his hands and knees. This is visible on the DVD as well as at the cinema. (00:05:50)