Continuity mistake: In the exterior front shots of Elliott's house there are some significant changes to the landscape in different shots. For instance, the two lampposts at the bottom of the driveway change to an entirely different style in some shots, and the huge garden boulders repeatedly vanish and reappear. Also, note when Michael takes off on Elliott's bike to go search for ET, the in-ground lamppost that should be beside the mailbox has vanished, but it reappears when all the government agents are setting things up outside the house.
Factual error: In World War 2 London, Pink is shown playing with an aeroplane model - an Avro York. The earliest available plastic model kit of this aircraft was produced in 1967. Inaccurate model aside, it begs the question of what a kid of Pink's age would be doing with a plastic model kit during World War 2 anyway.
Plot hole: Patrick Redfern needs someone to be in the boat with him to corroborate his and his wife's deception and be his alibi. That is whole point of his wife lying on beach - he gets this when taking Myra for a ride - but it was portrayed as a random ride she got, he did not intend or plan giving her a ride, he did not see her loitering near the boat, or even in view of him untying the boat. Even if that was intention in the story for him to be seen ready to cast off, the movie viewers did not see her viewing him, only her appearing just before he was set to cast off. Without someone with him the whole deception would not work, he would have no alibi, he could have killed Arlena unseen.
Audio problem: On the bridge, sounds of a nearby boat can be heard; however, a boat is never actually seen nearby, nor any lights on the water.
Factual error: I work for a television channel in 'daytime serial' production and I can assure you that no actor is going to secure a recurring speaking role in a soap opera unless a comprehensive insurance policy has been secured. (This applies to feature films, too.) This will inevitably involve a medical examination. I'm afraid Mr Dorsey's plans are going to become dreadfully unstuck the minute he drops his y-fronts in the doctor's surgery. (No, he can't find a compliant or bribeable doctor - the insurance company will always use their own people.).
Continuity mistake: At the start of the film, the dog is seen going from room to room looking for food. Just before he goes into Dana's room, someone can be seen through the crack in the door, moving from left to right.
Other mistake: When Deckard visits the Tyrell Corporation, he prepares to test Rachel with the "VK" machine. He is shown putting his briefcase of the table and lifting the "VK" machine out and onto the table. If you look closely, the "VK" machine is already on the table and Harrison Ford is miming the lifting - there is nothing in his hands! (00:19:45)
Other mistake: Rattner and DiMone are game planning about Rattner's date with Stacy (Leigh). DiMone tells Rattner that all he needs to do to score with Stacy is play songs from side 1 of "Led Zeppelin IV" (Zoso). You then hear the song "Kashmere", which is on the album "Physical Graffiti".
Revealing mistake: When the oldest son is being pursued by the unseen entity whilst the family is seeing the priest. You can see a crew member in green pants and brown shoes to the left as the camera perspective turns upside down.