Deliberate mistake: Clark's CPR form is terrible. When he performs emergency breaths on Lex, Lex's chest doesn't rise and fall, indicating that he's not actually breathing much air in. He doesn't bother to measure for the proper location for chest compressions, a very important step that is the difference between proper CPR and simply cracking ribs. As he performs compressions, he is not chanting the rhythm (one-and-two-and-three) and his elbows are bent. All of these were altered for dramatic reasons or the purpose of safety, but the sloppy technique probably would have killed Lex. (00:18:40)
Deliberate mistake: The episode begins with a football game in pouring rain. After the winning goal is scored, the crowd shots show the cheerleaders' hair wet and their uniforms completely dry. (00:01:50)
Deliberate mistake: When Clark is chasing Emily at light speed, Clark decides to use heat vision to knock the water tower down. The water tower shouldn't have had enough time to fall down and intercept Emily, seeing as she's travelling too fast.
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