Continuity mistake: When Sean emerges from the lake and goes to the campfire, his clothes are completely dry despite the fact that he was totally underwater for hours. (00:04:50)
Continuity mistake: When Chloe and Clark are at the Torch after the pool incident with Shawn, Chloe is sitting down wrapped up in a green sweater and a blue jacket with part of her blouse showing. In the next shot, she is fully wrapped in the green sweater. Seconds later, her sweater is tucked into her jacket and her blouse is showing. (00:28:00)
Continuity mistake: As Sean sucks electricity at the power station, his arms are bent in the first shot and fully extended in the next. (00:31:25)
Continuity mistake: When Sean is in the nurses office, having his temperature taken, the light on his left side is on. After the nurse wants to retake the temperature the light is now off.
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