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.
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)
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.
Continuity mistake: As Gant is pulling the Firefox out of the hangar, it is still very dark, as in pre-dawn. But as the Russian officers are shown shooting and watching the Firefox take off, it is suddenly much lighter outside as if it is after dawn and the sun can even be seen. But it would have taken 30-60 minutes for the light level to change that much.
Visible crew/equipment: When Alan and Lora go to see Kevin Flynn at his game room they find him playing his videogame 'Space Paranoids'. After he finishes playing, he turns around to talk with Alan and Lora. As they are speaking you can see the microphone coming up from the bottom of the screen. It even hits Kevin Flynn in the hand.
Continuity mistake: At one point in the film, the wingspan of Q is mentioned. Later on, its length is mentioned. The monster is twenty feet longer than its wingspan.
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)