Other mistake: Lex picks up a chisel and stabs Clark in the side. It bounces off and out of Lex's hand. The last couple inches are bent and twisted. Chisels are made from extremely tough steel. But no matter how hard Clark is, Lex is not strong enough to exert the force necessary to bend the chisel itself.
Other mistake: When Clark looks at Oliver's newspaper clipping, there's a story about an AIDS hospice being saved. But the 2nd paragraph on talks about the 2nd meteor shower to hit Smallville that has nothing to do with the hospice being saved.
Other mistake: When Jimmy wakes up in 1940, on his desk calendar it's Saturday the 3rd. The newspaper says it's May 3rd, 1940, but that was a Friday.
Other mistake: The bowling scorecard for Chloe and Lana is wrong. It shows Chloe knocking down 1 pin (-|1) in the first frame but getting 3 points, then a spare in the 2nd frame but only getting 1 point. The math is wrong until the 7th frame where is ends up showing the correct score. Lana's score is correct, except on frame 9 it shows she knocked over 6 pins on her first ball and is on her 2nd ball, but when it cuts to her, all 10 pins are up. Plus an unfinished 9th frame shouldn't show a score.
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