Continuity mistake: After Dante says "...if you want to turn that tortoise into a hare just give me a call." he walks off and the shot follows him as he walks all the way over to a black car and starts to work on it. The shot returns to Clark and Pete and Dante is shown walking away again on the left side of the screen.
Continuity mistake: At the start of the final race there is a bridge at the far end of the road that Pete and Jason are going to race to. During the entire race they never pass this bridge yet it ends up behind Jason's car when Pete looks in his rearview mirror as the crash is going on.
Continuity mistake: As the two racers speed past Clark and Martha, in the truck at the intersection, Pete's red car does not have its neon lights on in the back window and under the rear spoiler. Then in the next shot, while still racing, both the blue neon lights in the back window and the green neon under the rear spoiler are on.
Continuity mistake: As the car that Jason was in comes to a stop after the crash you can see Pete's red car is nowhere near the wreckage of Jason's car. In the next shot Pete's car is shown rolling forward to a stop, meaning he hadn't backed up but was still going forward and stopped where he was, but now Pete is only 30-40 feet from the wreck of Jason's car.
Continuity mistake: During the scene when Jonathan comes home from the hospital the length of rolled up sleeve on Jonathan's left arm changes between shots. As Jonathan says "Low sodium turkey?" the sleeve is down to just about touch the watch he is wearing. When the camera jumps to Jonathan's left side, as Martha turns around, the sleeve is now several inches higher and further from his watch than it was before. Jonathan does nothing to his sleeve between shots.
Continuity mistake: In Pete's rearview mirror there is only a couple of hundred feet between Jason's car, which is in the process of crashing at the time, and the bridge. In the next shot of Jason's car almost a mile away from the bridge. Drastically different distances.
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