Continuity mistake: When Clark and Alicia are talking by the ice rink, the way Alicia holds her red cup of hot chocolate keeps changing between cuts.
Continuity mistake: After Clark heats up Alicia's cup of hot chocolate with his heat vision, the steam coming from the cup is thick and rapid in the first shot, but in the next shot hardly any steam is coming from the hot drink.
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