Revealing mistake: There are times when it is quite evident that Michael Rosenbaum is voluntarily bald.
Other mistake: Throughout the series, they reuse the same footage for establishing shots of the Talon. For example, one of the shots has the Talon sign say "Silent Film Festival" with a guy holding and bouncing a basketball as they walk pass the Talon is in s02e05 and s03e11 and other episodes, including s03e10 where it's the same people but the guy is holding his jacket and further back.
Continuity mistake: The meteors are shown traveling together in space at the beginning, but the smoke trail from the first meteorite runs perpendicular to the flight of the next one. They should be falling along roughly the same flight corridor, as all the other meteorites do. (00:00:10 - 00:04:30)
Continuity mistake: In the truck right before the parade passes them by, Jonathan Kent kisses his wife. Cut to a different angle but this time his left hand is on her cheek. It wasn't there in the prior angle. (00:02:15)
Continuity mistake: After the meteor shower, the bit of hair that Mr. Luthor finds in the cornfield changes in his hands from stretched straight to curled. (00:06:15)
Visible crew/equipment: When Lex spins up to Luthor Corp in his car, as the camera pans over the car to follow him, the cameraman is reflected in the window as he pans over. (00:14:40)
Continuity mistake: When Lex is about to hit Clark with his car, Clark alternates between facing the car and facing the bridge. (00:17:20)
Factual error: Lex crashes and his car lands on its roof, but in the span of a few seconds it has sunk straight to the bottom, and turned the right way up. Cars don't sink that quickly. (00:17:25)
Continuity mistake: The hole in the guard rail changes size and shape between the shot of Lex driving off it and another looking up at it from below. (00:18:10)
Deliberate mistake: Clark's CPR form is terrible. When he performs emergency breaths on Lex, Lex's chest doesn't rise and fall, indicating that he's not actually breathing much air in. He doesn't bother to measure for the proper location for chest compressions, a very important step that is the difference between proper CPR and simply cracking ribs. As he performs compressions, he is not chanting the rhythm (one-and-two-and-three) and his elbows are bent. All of these were altered for dramatic reasons or the purpose of safety, but the sloppy technique probably would have killed Lex. (00:18:40)
Visible crew/equipment: When Clark finds Lex in the Luthor mansion, they walk down the hall and into a new room. As they enter, as Lex is saying "So, hows the new ride?" if you look in the bottom left of the screen you can see a white tape marker on the floor, where Lex will walk over to subsequently. (00:33:10)
Continuity mistake: When Jonathan lectures Clark about the danger of accepting gifts from Luthors, the key he twirls is a GM truck key, not a Ford truck key.
Audio problem: When Mr. Luthor was buying the corn field from the farmer he says: 'Now, where do I sign?' The farmer replies: 'Right here Mr. Luthor' and points at the contract. Even though we can only see a profile shot of the farmer as he says these words it is pretty obvious that his mouth isn't moving.
Continuity mistake: Despite the fact that Clark and Jonathan are looking in the rafters above them for Greg, their flashlights stay relatively level. (00:26:35)
Answer: The kryptonite only creates mutations when it reacts with the environment and an individual. Remember, the FDA and several environmental groups did check out Smallville after the meteor shower, but found no danger in the rocks. Obviously they're not always emitting mutating rays, or all the flora and fauna of the surrounding area would be horribly mutated.
Phoenix