In the kitchen, when Michael Douglas is preparing the hot water for the tea, just before the final bathroom fight, there is a shot of him looking up at the ceiling and noticing the leaking water (obviously from the overflowing bathtub). But, he turns back toward the stove and continues to prepare the tea, instead of having an immediate reaction that something is wrong. It is not until the teapot whistles, and his wife screams, that he realizes something is wrong. He should have run up stairs as soon as he noticed the water leaking from the ceiling. [Character choice, not a movie mistake. A slow drip of water from the ceiling would require attention, but with everything else on his mind he decides it can wait.]

At the beginning of the ridiculously scripted final climactic scene, Dan is downstairs in view of the front door, which is closed, while his wife is upstairs in the bathroom. As the wife is looking in the bathroom mirror, we see Alex suddenly come into view and begin to slowly approach her from behind. Assuming she entered the house the regular way, how did Alex get into the house and up the stairs without being noticed by Dan? The only other way would have been to somehow climb up the back of the house and break a second-floor bedroom window in order to enter; however, the wife would have heard this from the upstairs bathroom. Either way, Alex could never have made it to the upstairs bathroom undetected. [Alex could have been hiding in the house prior to Dan locking the door, his wife going upstairs or them even coming home. In fact, during the conversation with the police detective, he says that Alex is missing. Which suggest she could have been missing up to 24 hours, plenty time to break into their house and wait.]

Glenn Close's character is called Alex Forrest in the credits but when Douglas is looking through the newspaper and sees her father's obituary, his name is spelled Forest. [Newspapers misprint people's names all the time.]

As Ann Archer is walking in the kitchen before the famous revealing of the bunny in the pot, look closely behind her and in the window you can see something moving slowly outside that looks like a crane. [It is a garbage truck.]

When Glenn Close calls Dan in the middle of the night he even says.."it's 2:00 in the morning", when it pans to Glenn Close talking to him, her apartment is lit up with sunlight and you can see the sun rays through the window. [Her apartment is lit up because she has her lights on. What's coming in through the window could be from a street lamp.]

The shots of the exterior of Michael Douglas's Long Island home and the shots of the interior are from two different houses. This is most obvious because the front door has two windows on the top of it in the exterior shots and the interior shots show a door with one window. Also, when moving a couch into the house, the workers are shown coming into the house from left side of the porch, which is impossible because the exterior shots reveal a wall on the left side. [The exterior door with two windows is a side door. The interior door with the stained glass and off the open porch, is the front door, which they seem to use throughout the movie.]