Revealing mistake: The two sets of steps visible from the front of Richard's house (to the right of the garage) are awkwardly placed and unrealistic. Several steps are perpendicular to Richard's parked Jeep then disappear behind the trees. The second steps are parallel to the Jeep (but perpendicular to the other steps) and appear to start "in the air" near the top of the garage, are at an odd angle to the deck and would lead to the side wall of the house's exterior above the deck, not the deck or front door. (00:03:35)
Revealing mistake: When Gregory throws Tree through the window during the final fight, as Tree lands, you can see the outline of a stunt-pad on her thigh beneath her pants. You can also tell it's a stunt-woman, as her body is slightly stockier than Tree normally is.
Continuity mistake: The location and intensity of Lavinia's purple hair highlights vary throughout the movie. For example, the purple highlights on the right side were far more pronounced (two wide, distinct, vivid lines) when she got home compared to when she first met Ward. Lavinia rode her horse Comet home, so her hair would have been wind-blown and the highlights would not have been likely to be neatly straight down, especially since she has long curly hair. (00:05:10 - 00:07:13)
Deliberate mistake: Carson's [John Travolta] cat Raymond did not appear to be in the pet carrier when he was running out of the building to his car or when walking to his office and placing the carrier on the desk. (00:02:15 - 00:03:30)
Continuity mistake: Scooby and Shaggy are lying face down on the massage table when the zombies arrive. Shaggy has his robe lowered baring the upper back, but in the close-ups you can still see the robe up covering his shoulders perfectly. (00:28:00)
Other mistake: Jethro said to Brian, "Shall I tell you how I know you're lying? Because when you said that, you looked up to your left." However, Brian looked to his right and Jethro even pointed to Brian's right when he was telling Brian that he looked to his left. (00:56:00)
Continuity mistake: The spacing (almost touching versus several inches apart) and appearance (shape and whether there are shoots) of the two flowers in the vase on Estelle's/Betty's table at the restaurant vary. Sometimes, the flowers on her table look more like the ones that could be seen on the table in front of hers after Brian/Roy entered the restaurant. (00:03:40)