Continuity mistake: When Tyler injects Brigitte for the first time at the hospital, look carefully at the syringe. You'll see that in the first shot its content is 1/3, and in the following shot is now 1/2 full.
Continuity mistake: When the girls are looking for food in the container, the blouse straps from the girl on the left change position frequently.
Continuity mistake: Near the end of the movie, Kate's hair is wet and she has a bloody nose. When she finds the platform again her hair is a lot dryer is and her nose is not bleeding.
Continuity mistake: When Joey is participating in the concert he goes along with pretending to be cut up. His jeans are clean until they put him on the glass table, when they're covered with fake blood. In the next shot, they're clean again and they start to cut him apart with the fake chainsaws.
Continuity mistake: When Lynn first finds out about the Olson murders, their house is two doors down from where she is house sitting. Later on, when Detective Peters mentions the murders in passing, he states that their house was three doors down.
Continuity mistake: When Ash breaks the window in the house at Long Island all the glass disappears in the window, apart from a little at the top. However, in the next shot when Telly and Ash walk through the window, all the glass has vanished.
Continuity mistake: After the sergeant has a parasite bug forced into her, she grabs a syringe kit left on the table by the medic. When she flips it open, there are 7 (maybe 8 at most) syringes in the kit (the last one is broken). A few moments later, private Sandee follows a trail of syringes left on the ground to the sergeant. There are at least 7 syringes on the ground, and 3 others in the sergeant's thigh.
Continuity mistake: When Kirstie Alley is having a breakdown on the news set, the arrangement of the yellow papers next to her changes between shots.
Continuity mistake: Nell writes a note to Julia after she misses their morning run. Between shots the handwriting of the note changes - the letters are different in spacing and size. (00:46:35)
Continuity mistake: The amount of dirt and blood on Tina's face and hair constantly changes between shots, from a lot of dirt and blood to some dirt and blood, to none at all.
Continuity mistake: When Agents Mackelway and Charelton are driving to the scene where there is a murder victim in a car hanging at the edge of a cliff, we can see the dust trail from the car begin about 50 yards up the dirt road. With as little wind as there was in this scene, we should be able to see dust all the way up the road. Also, when they start talking with the local sheriff there is a very noticeable cloud of dust behind them, there is a brief cut away, then the dust cloud is totally gone.
Continuity mistake: When Bridgett says "Ginger, we've lost our way " in the beginning, Ginger goes from looking forward to looking to the side between cuts.
Continuity mistake: When mixing drugs to overdose the others in their kitchen, while wearing a gas mask, Richard (soldier) has long hair, yet throughout the rest of the film he has short shaved hair.
Continuity mistake: In the scene where Rennie drives to the "Towers Motel" in the exterior shot the car is casting a shadow to it's left. In the next shot (interior view), the trees standing outside cast a shadow to their right.
Continuity mistake: Simon gets groceries, carries them home in two bags, and is then in the hallway without any groceries. It is never clear that he sets them down. (01:20:35 - 01:21:40)
Continuity mistake: When Luke is searching through Roger's belongings, looking for any alien "remains" from his encounter, he lifts up Roger's mattress revealing porn magazines. In the next shot the magazines are all differently positioned and much more spread out than in the first shot.
Continuity mistake: Throughout the movie, Cottonmouth Joe's horse changes from a tan Arabian to a black Clydesdale during attack sequences.
Continuity mistake: When the protagonist goes to the mental institution and meets her former classmate now plagued by asthma and violent overacting, a wisp of hair on the forehead changes position between shots a couple times during the scene without her touching it or moving. (00:46:25)