The Faculty (1998) - 25 mistakes
Directed by Robert Rodriguez, starring Bebe Neuwirth, Famke Janssen, Robert Patrick, Salma Hayek
Continuity: In the scene where Casey is walking up to the school after his father drove him there, we see that Casey's bagstrap is backwards. Then they cut to the car, and when they cut back to Casey and all of a sudden, his bagstrap is turned the right way. The next cut is when coach Willis and Casey's father look at Casey and then Casey starts to walk up to the school again and his bagstrap is turned backwards again.
Continuity: In the scene where Zeke is in his car driving and fighting off Miss Burke, just before he crashes into the bus, you see him inside the car struggling to buckle his seat belt and therefore with all hands on it. Problem is, the camera filming the car from the outside clearly shows that the driver has both hands firmly gripped on the steering wheel and is swerving out of control.
Continuity: In the scene where Marybeth tells Zeke that he couldn't be sure what he saw when they were all taking the drug-test to see who was an alien, we are shown a flashback of her using a weird extension on her alien finger to cut the blue end of the tube off and let the powder pour away. In the flashback, the blue end falls on the floor and is gone. Yet if you watch the first showing of this scene, when they were actually taking the drug test, we see a very clear shot of Marybeth just after taking the drug, and the blue end of the tube is intact.