Continuity mistake: When Jason starts knocking on Lana's door, the clasp from the door chain is all the way to the left. The camera cuts to Lana in bed. When it cuts back to the door, the clasp is now all the way to the right.
Revealing mistake: Kristin Kreuk's body double in the shower scene is noticeable. She is slightly larger and differently shaped.
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.
Factual error: There is a snow pattern on the Quicktime player after Chloe's message to Clark finishes. She would have recorded in on a camcorder, so there wouldn't be any snow pattern, it would be a blue or black screen. The only way there could have been is if she recorded it, put it on VHS, then copied it back onto a DV tape, then transferred it back onto her computer, but there's no reason for her to do this.
Continuity mistake: While Martha reads to Jonathan, as he is in a coma, the light on his hands change. In the shot from the right side of Jonathan's bed his hands have only a normal level of light like from a small table lamp. The shot changes to look at Jonathan from the doctor's point of view and suddenly Jonathan's hands are very brightly lit like from a spotlight. No one changed or turned on any other lights between shots.
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