Revealing mistake: In the scene in which Jonathan shoots Lex, he is gently lowering and raising the barrel of the gun whilst shooting, even though there is a 'bullet-time' effect in progress. Maybe the sequence is shot in real-time, with the actors standing still and the 'bullet' added afterwards? Furthermore, would Lex really move that quickly in relation to the speed of the bullet?
Revealing mistake: As Sheriff Ethan pulls up there is a reflection on his driver side window. You can see the police department shield on the door and the door handle reflected on the driver's side window. There were no other police cars there so it was probably reflected off a mirror used to help light the scene.
Revealing mistake: In the sheriff's office, the door to the jail area has no lock plate on the wall.
Insurgence - S2-E12
Revealing mistake: After Lex's employee walks out of the office, Lex gets mad and throws most of the objects off his desk. Prior to this, we see a computer screen displaying something. When the objects go flying off and hit the wall, we see that it wasn't actually a computer screen but a prop that was made look like one. It was just the frame, a piece of paper that served as the display covered by clear plastic to make it look like an actual computer screen.
Revealing mistake: When Tina puts the necklace on Clark to disable him, he falls to the ground of his barn. As he is lying there, his collar is very dark, and his shoulder is lit up. Since the source of the green light is supposed to be the necklace, his collar should be the brightest lit.
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.
Revealing mistake: When we see Ian split, his two selves are supposed to be looking directly at each other but they're really both looking slightly to the right. It's hard to focus when there's really nothing there. (00:15:45)
Revealing mistake: In the Talon when Crissy is talking to Clark, we see a close up of her hand aging. However, as her hand ages, a reflection of her real hand (which supposedly aged) can be seen on the metal clip of her clipboard, which is still young and smooth, and not aged.
Revealing mistake: When Lionel is playing the piano while talking to Lex, you see inside the piano and none of the dampers are moving for the notes he's playing, revealing he's not really playing or even hitting the keys.
Revealing mistake: When Pete is on his motorbike they pan to his face and we can see the stunt double. (04:36:00)
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