Continuity mistake: When Kal-El/Clark pushes Martha away her hands are down around her chest. The shot changes, as Kal-El builds up power to fly, and now Martha's hands are spread out away from her body.
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.
Phoenix (2) - S3-E2
Continuity mistake: When Clark and Jonathan return home, Jonathan collapses on the couch. It shows Clark rushing to his side. But in the next shot where it shows Martha's reaction, you can see Clark rushing to his side again.
Exodus (2) - S2-E23
Continuity mistake: When Clark is fighting with Dr. Walden, twice Dr. Walden sends Clark flying, with his powers. Both times, when Clark hits the ground, he becomes quite buried into the soft dirt, not entirely, but relatively sunken into it. However when it will cut to the next shot, Clark is lying on the dirt without being buried into it at all. This is obviously due to switches between actor and stunt double.
Vortex (2) - S2-E1
Continuity mistake: When Clark brings Lana to the hospital, a doctor attends to her and checks her vitals. In a close up we see the doctors right hand on Lana's neck checking her pulse and her left hand is no where in sight. Cut to a wider angle (as Clark runs away) but now the doctor is holding a flashlight in her right hand and her left hand is on Lana's forehead.
Audio problem: Clark is upset over the death of Alicia and is in the barn loft bouncing a ball off the wall. His parents come up and Jonathan sits next to him and tells him that what happened was not Clark's fault. The very next shot shows Martha sitting down and you hear Clark throw the ball again but you can see that his hands never make and motion to correspond with that action.
Continuity mistake: When Clark and Lex were talking about Helena while playing billiards, Clark picks up the stripped blue ball. They then continue to talk as he plays with the ball in his hand. He then puts it back on the table allowing it to roll but now its has changed into the cue (white) ball and the stripped blue ball can be see in the foreground right next to the side pocket and a stripped red ball.
Continuity mistake: The shot with Ian pulling Lana out of the car shows the shadow cast on the bridge covering half the road. A few seconds later, after Chloe gets free of the Ian that has her, the shadows on the bridge are much shorter.
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: When Pete and Clark go to Byron's house to find him, Clark finds the hidden locked door to the cellar. Clark then breaks the locks and uses both his hands to pull on the door. Cut to a different angle (from above Clark) but now he is just using his left hand.
Continuity mistake: As Justin turns the spike end of the pathway light towards Principal Kwan, in the close up, the light is at a height that is just lined up with the light in front of it. After the shot change, the shot simply zooms out to include Justin on the right side of the screen, the light is now several feet higher than it was before.
Continuity mistake: When Lana and Clark are sitting on the Windmill and the camera is facing them close up you can see the shadow of the windmill moving in the wind but when the camera zooms out the windmill is not moving at all.
Continuity mistake: When Henry falls into the pond, the first time, there are several small pylons connected by a chain when the camera is on the walkway. When the camera is in the water, showing Henry as he hits the water, neither the pylons or the chain is visible. There is just an open space where the chair falls over.
Visible crew/equipment: As Chloe is running from the truck there is a shot where you can see the camera shadow on her back as she is completely turned away from the truck.
Continuity mistake: While Lana is climbing the windmill, just before she stops a shot from below shows her right foot right above her left foot. The camera switches to above her and suddenly her left foot is a full rung above her right foot. (00:27:10)
Vortex (2) - S2-E1
Continuity mistake: When Clark and Lex are searching for Clark's dad, right after Clark gets mad at Lex and leaves it shows a head shot of Lex with the bandage over his left eye. In the beginning of the show he was injured over his right eye. (00:15:30)
Factual error: When Clark is on the roof, and Lionel calls him over to walk to his car with him, in the background as they walk, you can see a building which has the logo of a Canadian bank. Although set in Smallville and Metropolis, Smallville is filmed in Vancouver.
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