Audio problem: After Clark is dumped into the blast furnace and the thieves make a getaway in their truck, you can hear the sound of an accelerating engine as it's driving away, but the brake lights are on.
Revealing mistake: Clark tries to stop the three guys who are inhaling refined kryptonite. As Clark gets tossed through a window, you can see the explosion of a small charge in the bottom left of the widow. Highly noticeable since Clark hits nowhere near where this charge goes 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