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.
Continuity mistake: In the closeup when Zoe is introduced, the button just above her apron is buttoned. In the next shot of her walking through the cafe, it is unbuttoned. (00:07:35)
Continuity mistake: As Harry goes into the pond the second time the pylons are connected now with yellow crime scene tape when the camera is out over the water looking at Harry on the walkway. As the camera is in the water, watching Harry fall in, the pylons are gone, even though they should be in the shot, and are connected by a wire instead of crime scene tape.
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