Continuity mistake: In his office, Michael Douglas looks up Hazel Dobkins' name on the police computer. Gus Moran comes in to speak to him and the pencils in the pencil holder move between shots without anyone going near them. (00:45:35)
Continuity mistake: As Michael Douglas chases Sharon Stone down the highway his car almost has a head-on collision with a speeding bus and if you look closely in the second shot that we see of the bus, it's not moving. (00:41:05)
Continuity mistake: In the first scene of the movie Sharon Stone holds the end of her white silk scarf in her right-hand. In the next shot the end of the scarf is draped over her right hand. (00:03:25)
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.
Continuity mistake: At his apartment Michael Douglas takes his sunglasses off and puts them down on the counter where Sharon Stone later breaks up a big hunk of ice for their drinks. The glasses rotate 45 degrees throughout the scene without anyone going near them. (01:04:00)
Continuity mistake: In the first scene of the movie Sharon Stone ties Jonny Boz's right hand with her white silk scarf. When we first see his hand it's wide open than in the next shot it's closed only to open as she pulls the knot tightly. (00:03:35)
Continuity mistake: When Michael Douglas walks into Jeanne Tripplehorn's apartment we see a chair on the left of the screen. Later in the scene the chair is pushed right up against the table, which it wasn't in the previous shot. (00:35:30)
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: Michael Douglas waits in the dark in Jeanne Tripplehorn's apartment and says to her after she walks in, " Tell me about Catherine". At first we see a couch and chair on the right side of the room but two shots later as he walks towards her these two items have been removed from the room. (01:38:40)
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: No definitive answer is given in the film. Catherine didn't need a reason for anything that she did. As for Beth, that was just a bonus, or a coincidence. It could be argued that Catherine targeted Beth, and Nick was just unfortunate to be involved with Beth.
ChristmasJonesfan