Revealing mistake: When the Enterprise is leaving its docking station and pulling out, two little bugs or debris from the model lands on the camera lens on the lower left corner (corrected in the Director's Edition).
Revealing mistake: You can see the stick making the finger move when it's in the box. (00:38:20)
Revealing mistake: As Holmes and Watson are riding home from Watson's stay in prison, in the background double traffic lines are visible as are concrete traffic barriers. These are a modern invention and out of place.
Revealing mistake: You can see Jackie's knuckles are already bloody BEFORE she starts pounding on the closet door.
Revealing mistake: When Dr. Menard is driving and discussing the zombie plague with the visitors, the "clean" part of the jeep's windshield (i.e. the path of the windshield wipers) appears to be cut out of the glass (probably to provide a better view of the actors and prevent the camera being reflected on the glass).
Revealing mistake: At the end of the movie, when Ben stakes vampire Susan in the heart, she throws her head back in pain and you can see her real teeth behind the fake vampire teeth.