Continuity mistake: There are several close up shots of the syringe that Dr. Hamilton is using to threaten Pete with and you can see that it is made of plastic. Clark uses his heat vision to overheat the syringe causing it to burst but the sound the syringe makes when it bursts is that of a glass syringe and not the plastic one he was actually using.
Other mistake: Early in the episode, Clark uses his heat vision to blow up a police car. In the shot where we see the policewoman diving for cover, there is a front view of the car as it is exploding. The license plate on the front of the car IS a Metropolis plate, however, as the plate falls off, the white placard that auto companies and dealerships place in the license plate frames on new vehicles before they are registered and which are removed once plates are installed is visible.
Continuity mistake: At the end of the episode, Perry and Clark arrive at the intersection to wait for the bus. They walk out into the intersecting road, and the bus arrives, positioned in the middle of the road, since they are standing in the right lane. Perry and Clark say their goodbyes, and a new shot of the bus from behind, shows the bus is in the right lane only as it starts up from the stop.
Factual error: In the 5th season episode "Lexmas," Chloe says she needs Clark to deliver the Daily Planet's Toys For Tots contribution because of a Teamsters' Strike. However, the Toys For Tots program is run by the United States Marine Corps Reserve, and collection and distribution is handled by Marines and Reserves. The Teamsters have nothing to do with it.
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Other mistake: Lex picks up a chisel and stabs Clark in the side. It bounces off and out of Lex's hand. The last couple inches are bent and twisted. Chisels are made from extremely tough steel. But no matter how hard Clark is, Lex is not strong enough to exert the force necessary to bend the chisel itself.
Continuity mistake: During the scene where Clark and Knox fight, Knox smashes his blue container with his weapon. Shortly after this, there is a shot where he is looking in horror at what he'd done and behind him, Chloe is struggling with her ankle cuffs. She appears to be wearing shoes in this frame, whereas before and after, she is barefoot.