Revealing mistake: When Jack is hanging out of the truck you can see him standing on the hood of the car which Lydia is driving. At some points we get camera view from the back seat of the car. In some angles the mirror inside the car disappear. This is to prevent us from seeing the camera.
Continuity mistake: When Jack is having a seizure at his job he stuff some aspirin in his mouth. When the manager says "He is spaced out." it cuts to the girl saying "I'll handle this.". At that point Jack has got two aspirin hanging out of his mouth. It cuts and the aspirins are gone.
Trivia: The filmmakers used two different shopping malls for the scene where the doctor injects Tuck into Jack's rear. The opening scenes where the doctor runs in and heads for the elevator were shot in the Northridge Mall in the San Fernando Valley in Los Angeles. The scene where he reaches the top and rams the syringe into Jack was filmed on the top floor of the Sherman Oaks Galleria, another mall several miles away.
Trivia: After Scrimshaw and Canker are shrunk 50%, there are a few scenes where they are seen with full-size actors. These shots were actually filmed using forced perspective. For the car scene, the rear of the car is actually twice as large as a normal car rear, and was about 20 feet away. During the scene half size hands and double-size heads were used. Using this method, the film-makers didn't have to worry about compositing two separate shots in post production, so the shots could be completed quicker. Even in the final scene with the suitcase, the case was twice as large, but the hand that closes it was real, closer to the camera in sync with the closing. (It took about 20 takes before it was perfect).