Continuity mistake: When Jonathan runs up to Lex, while he is unconscious, the first shot of Lex has his arm bent but not near his face. The shot switches to look down on Lex and now he is laying with his hand considerably closer than the previous shot.
Continuity mistake: When Lana shows Chloe the picture of her mother and Henry Small. We see that Chloe holds the picture on its bottom corners with both her hands. Cut to a close up of the picture but now she is holding it in the bottom middle of the picture. Cut back to the previous angle and she is holding it by the corners once again.
Continuity mistake: When Lex comes to after being kidnapped by Rachel, she wipes his face with a piece of cloth using her right hand. She then transfers the cloth to her left hand and continues to wipe Lex's face. Cut to a different angle as she says "I bought it with the money your father gave me" but now the cloth is instantaneously back in her right hand.
Revealing mistake: As Sheriff Ethan pulls up there is a reflection on his driver side window. You can see the police department shield on the door and the door handle reflected on the driver's side window. There were no other police cars there so it was probably reflected off a mirror used to help light the scene.
Continuity mistake: In the flashback when the Kent's meet Clark, we see Jonathan loading the space ship onto the back of the pick up truck. He then see Martha carrying Clark who was wrapped up in a blanket. At first we see that Martha's left arm is wrapped around Clark's back onto his shoulder. Cut to Jonathan's viewpoint and now Martha is just supporting Clark and her left arm is no longer around Clark.
Continuity mistake: Lionel press conference about Lex's kidnapping only infuriates Rachel. She then picks up an axe and was about to swing at the tied up Lex when he manages to get his right leg free and kick Rachel backwards. As she falls backwards, we can see that she drops the axe off to her left side. Cut to a different angle but now the axe is over her head to her right side.
Continuity mistake: As Jonathan and Martha drive away in the truck, we see Rachel for the very first time and she has both her hands in her coat pockets. Cut to a close up but now her hands are outside the coat pockets.
Continuity mistake: The woman uses her right hand to get a swab for DNA testing from Clark. At first, we only see her right hand near Clark's face. Cut to a different angle as she says "There, now that didn't hurt a bit did it?" but now her left hand is close to Clark's face.
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