Plot hole: At the very end of the film where Dr. Challis sneaks behind one of the computers and turns on the "commercial" in hopes of destroying Cochran and all of his robot employees, once the commercial starts you see some of the employees panic and go into hysterics and try playing around with the computers to try and stop the commercial, but they seem to not know what they are doing. However, though only 20 minutes earlier, Cochran's employees knew exactly how to start and stop the commercial perfectly when doing the "test" on little Buddy and his family.
Factual error: Towards the end of the movie, we see Dr. Challis hide amongst some boxes when running from Cochran's men. Challis then finds a phone on the wall and dials his ex-wife, attempting to warn her of Cochran's plans. When he dials her, he only pushes 5 buttons on the phone. Even without an area code in the United States, all phone numbers have always had 7 numbers.
Other mistake: Why is it that Marge only discovers the microchip in the Silver Shamrock badge when it drops on the floor in the motel room? Surely she would have noticed it when her son would have thrown the mask against the wall, and it dropped off? Any normal person would have looked at it to see how it would have attached to the mask.
Continuity mistake: During the scene where Dr. Challis is outside talking to the bum, the camera shot from behind shows us Dr. Challis taking a huge drag from his cigarette as the bum is talking about Silver Shamrock having its "last Halloween." A split second later, the front camera shot now shows Challis replying to the bum, but no cigarette smoke is being exhaled from his mouth, as it should be.
Revealing mistake: Watch closely during the scene where Ellie Grimbridge arrives at the hospital room to id her dad Mr. Grimbridge, who the night before had been murdered. As she says, "Let's get it over with", there is a door behind her. On the door is a tag which has the room number. The shadow on the door is about 5 inches BELOW the room number tag. A split second later, the camera switches to a shot of Dr. Challis watching Ellie, and then back to Ellie and the door. The shadow is now EVEN to the room number tag, meaning the scene was probably shot a half hour later, yet the sequence of happenings was only a few seconds.
Revealing mistake: At the beginning of the movie we see one of Cochran's assassins enter Mr. Grimbridge's room at the hospital to gouge out his eyes and rip his skull backward. The assassin then wipes the blood from his gloves on the curtains. However, when the camera pans back to Mr. Grimbridge, he is just squinting his eyes closed really hard, and if you look close, his eyelids flinch a little bit.