Continuity mistake: During the interrogation scene, Stone has her legs crossed right over the left then suddenly left over the right and a second later (during the shot where she wears no underwear) right to left again.
Plot hole: This is another movie where the cops are too dumb to go out by themselves. The woman who icepicks the first victim (we see) to death would have left enough forensic evidence on the scene to convict her ten times over - skin, hair, sweat, saliva, vaginal fluid, possibly blood, and they all contain DNA in abundance. She had vigorous, sweaty sex with this man and she didn't clean up afterwards (and she couldn't have done so thoroughly enough anyway) so she's left calling cards all over the place. The killer also handled the icepick (which the police take away in an evidence bag) with bare hands - her prints would be all over it. She might as well have left a signed confession, but they can't even identify her. Sharon Stone, for instance, leaves her fingerprints (on the chair and fixtures in the police station) and her saliva (containing epithelial skin cells which are an excellent source of DNA) on the cigarette butt she discards, also in the police station. She went there of her own accord and these artifacts are legally accessible by the police. It is obvious to anyone that the women who had sex with the victim killed him, and Catherine is most certainly a suspect. They don't have enough to charge her but they would if they did a simple series of tests on the dead man's body - and if she didn't do it, that would eliminate her as a suspect. They don't even check.
Continuity mistake: As Michael Douglas and his partner drive Sharon Stone to the police station for questioning in the shots of her she's sitting on the left of the rear window. When Gus Moran looks at her in the rear view mirror she's on the other side next to a large police light. Throughout the scene she moves left and right between shots on the back seat. (00:23:00)
Continuity mistake: In the scene where the actual murder takes place the blonde woman stabs him in the neck. The body has no blood on it. The second stab the body is covered with blood. This all happens in one eyeblink.
Continuity mistake: Douglas opens a mailbox to check the mail for clues. He then puts the mail back and closes the box, a second later you hear him closing the mailbox again.
Continuity mistake: Michael Douglas goes back to Sharon Stone's house where she invites him upstairs as he watches her break up ice cubes with an ice pick. If you look closely at the painting above her fireplace, you can watch the different times of day go by between shots in the reflection of sunlight off of the pool and onto the picture. (00:47:10)
Continuity mistake: When Roxy runs off the bridge you see the Lotus crashing over with its low beams on - when you see the car fly off the bridge its brights are on.
Continuity mistake: Sharon Stone leaves the top of Michael Douglas' back all bloodied with her sharp fingernails. After the lovemaking scene, Roxy talks to him in the bathroom and we see the reflection of his back in the mirror. The scratches on his back are now much lower and not anywhere near the right place. (01:13:25 - 01:16:10)