Continuity mistake: When the detectives ask Catherine to go in for questioning, she has her hair down. Then, a minute later, she comes out with her hair up. Problems: one, there's no way Catherine could do that on her own, and no-one else is in the house; two, even if she could it would take much more than a minute, say thirty minutes.
Continuity mistake: When Nick and Gus are waiting for Catherine to get changed, out of the corner of his eye, Nick sees Catherine step, naked, into a white dress, then, again, she steps into the same dress.
Factual error: The road where the cops drive on their way back from the beach - where we see San Francisco in the background - is a dead end. It does not lead to Stinson Beach.
Continuity mistake: When Michael Douglas and his partner are in the diner, the cap on the Tabasco sauce bottle is off. A second later, it is on.
Continuity mistake: In the scene where Rocky and Nick are talking in the bathroom you can see Nick's back in the mirror - he has two nasty looking scratched up areas of bare skin on his back - then when he turns and returns to the bedroom you can see that he now only has a couple of superficial marks.
Factual error: The light reflections at Tremell's beach house are not the ones an ocean would make. The reflections are from large flat areas of almost calm water - like in basins - but there are none around.
Character mistake: When Beth encounters Nick after Gus has been murdered, she puts her hand in her pocket and steps forward, prompting Nick to order her to freeze and to take her hand out of her pocket while aiming his gun at her. However, she just keeps reaching for what's in her pocket and approaching Nick, resulting in him shooting her. Considering that she works on the police force, she absolutely should have known for a fact that she was being suspected of reaching for a gun, but thinks nothing of it.
Other mistake: Beth gives Nick his keys, saying he left his keys at her place, meaning they're his keys, but then she takes them with her, and those were the same keys she had in her pocket when she was shot.
Factual error: When Nick is looking up information about Hazel, the computer says she was released from San Quentin. That's a men's only prison.
Character mistake: When we see the door to Elisabeth's, her name is spelled with a s. Later when Nick looks her up on the computer, it's spelled Elizabeth.
Continuity mistake: At the beach house, Catherine is cutting up a large piece of ice with an ice pick. Depending on the direction of the camera, the ice changes size: in one shot it's all together; but in the next shot there's a large chunk pushed to the left of her.
Continuity mistake: During the first sex scene between Michael Douglas and Sharon Stone, Miss Stone's nipples at first are very erect, but in the next shot are not.
Continuity mistake: When Nick and Gus are driving Katherine to the police station for the first time, they drive past the same stretch of coast about three times throughout the scene. Most obviously seen by the position of the small island - it jumps from being in the distance, to being even with the car, then behind the car, then in front again etc.
Answer: There's no definitive answer to this and the ending is deliberately ambiguous and open to interpretation. The audience is left to speculate whether or not Catherine kills Nick, or if she intended to kill him but changes her mind because she loves him, or intends to kill him at a much later time, and so on.
raywest ★