When Annie and Rhodes are on the side of the road with the radar, Rhodes says for her to aim at the license plates of the cars, which gives the best reading. This is not true, as radar is a frequency that emits a cone that will respond to any moving object within range, and its range is infinite. Radar doesn't react to reflective license plates, but to moving objects.
When Annie receives the shower invitation it reads "Sat." as the day. When Annie's car breaks down on the day of the shower, and Ted picks her up, she asks him, "Were you busy?" and he answers, "Well, it is Friday."
When Annie leaves the bridal shower, followed by Lillian as she leaves the backyard to walk through the house, she is wearing shoes, and you can hear the sound of the shoes as she walks on the floor. But when she walks out of the front door moments later, she is barefoot.
When Annie is asking Rhodes to help them find Lillian, when Rhodes is standing at her car door he has what looks like a couple days worth of stubble on his face, but when he is back in his squad car, he is clean-shaven.
When Ted pulls up to give Annie a ride after her accident, his car seats have the optional Porsche crest on the headrests. But in the interior shots after she gets in, the crests are gone revealing that two different cars were used.
When Annie and Helen are singing a duet of "That's What Friends Are For", during the last verse, Annie has the champagne in her left hand and the microphone in the right. In the next shot, she has them reversed.
While Annie is making the carrot-shaped cake, she uses a liquid measuring cup instead of the dry measuring cups for the flour. She pulls them out of the kitchen drawer but the next shot she is using a liquid measuring cup to pour flour in bowl.
After Annie leaves the bridal shower, she is seen driving down a two lane rural road. Megan, with numerous puppies in her van, pulls up next to and passes Annie. The street they are driving on suddenly has changed to a five lane highway with a more urban background. Megan pulls in front of Annie and speeds away. Seconds later, Annie slams on her brakes to avoid hitting a porcupine, and once again is on a two lane rural road.
When Lillian is opening her gifts at the bridal shower, Megan's hand brace is on the wrong hand. During this scene it was on her right hand, while during the scenes before and after it was on the left hand.
When Officer Rhodes is talking to Annie and Helen on the side of the road in the shot looking into the car (from Rhodes' POV) his hand is on the frame of the car. But from Annie's perspective (looking at Rhodes) his hands are by his side. This happens numerous times throughout the scene.
The plane seen taking off to Las Vegas has two engines and appears to be a Boeing 767. However, when the plane makes an emergency landing in Wyoming, the plane seen landing is an L-1011 (three engines; the third mounted via S-duct in the tail).
Twice throughout the film the Officer Rhodes says the names of intersecting streets in which characters live in Milwaukee, but when the location is shown, the street signs have different names on them.
When Annie and Rhodes are on the side of the road with the radar, the radar is actually a Kustom Signals HR-12 model which is not wireless. The cord has been removed, meaning that what Annie is holding is a dead, non-working unit.
The Wilson Phillips CD Lillian gets as a present is a greatest hits compilation featuring the song "Hold On", rather than the original album this song appears on. It isn't the wrong CD, just a different one.
Megan turns on the camera to record the sexual encounter with air Marshall Jon. At first she is very close as if camera is on a tripod, and she has just started recording. Next we see camera movement which is clearly being filmed by a second person.