Continuity mistake: After Lois hits the dog, she exits her car and runs to the dog. As she passes the back of the car, her tail lights are off. When she reaches the dog, her tail lights are on.
Continuity mistake: As Lex is chalking his pool stick while talking to Dominic about cutting 20% of the workforce at the LutherCorp Smallville plant, there is a red snooker ball on the wall rack missing from the second row. When Lex walks over to the other end of the pool table, the camera shot changes back to Dominic, now there is a ball missing from the top row, which was not missing before.
Continuity mistake: While Clark and Jonathan are talking about Clark being on the football team, Jonathan puts his hands on Clark's shoulders. Between shots, the position of Jonathan's hands on Clark's shoulders repeatedly changes.
Audio problem: Near the end, when Clark is surprised by the woman coming to say good bye, as he is working on the tractor the distinct sound effect heard is that of a ratchet wrench, but what he puts down is a normal wrench, not a ratchet wrench.
Continuity mistake: When Lois and Arthur are sitting at the end of the dock, (before Arthur begins to hear the piercing ringing sound) the position of the bikini lace hanging down Lois' back keeps changing between shots.
Visible crew/equipment: Episode 22, Season 5 - "Vessel": Lex returns to the mansion, after being abducted, with his new powers. When he shows Lana by shooting his hand, they start talking by the stained glass window. The reflections in their eyes are supposed to be the light coming through the window, but are actually from a white screen used for lighting. The reflections in their eyes are rectangular to confirm this.
Continuity mistake: While Earl is in the hospital bed, his grip on the microphone to the waiting room changes from up to down and back. (00:17:55)
Continuity mistake: In the scene between Martha and Clark near the end of the episode, the cut on Martha's forehead switches from above her right eyebrow to her left, and then back again. (00:37:40)
Continuity mistake: In Episode 22- Season 5 - "Vessel": At the start, Lex wakes up and heads towards an open field many miles away from the mansion. They show a camera shot of his face in the field and the sky is grey and cloudy, but in the very next shot the sky has turned blue and the sun is shining.
Continuity mistake: After Lionel and Professor Willowbrook finish talking Clark shows up to talk to the professor. As they talk, while the camera is behind Prof. Willowbrook, he has bright sunshine on his suit coat. When the camera is behind Clark the light on Prof. Willowbrook's right shoulder is gone.
Continuity mistake: After Clark gives Chloe the piece of paper with the list of cars that checked into the hotel, Chloe holds the paper in front of a folded up newspaper. Between shots, the newspaper turns the direction it faces. Then in the next shot, Chloe is only holding the piece of paper, and the newspaper that she was holding behind it has now disappeared.
Plot hole: Chloe writes her phone number on Sean's hand. It disappears when we see him struggling against the ice of the lake, then reappears in the scene where he is calling old girlfriends. And how exactly would pen ink survive several hours submerged in water and then another eight hours of normal activity without becoming blurred? (00:04:15 - 00:19:50)
Continuity mistake: Lana looks over the edge of the crater and there is a fire right in front of her on the inside rim of the crater. When the shot changes and pans up to an overhead view of the crater and ship that fire is missing.
Continuity mistake: When Clark lifts Lana back onto the bridge, from a shot from above, we see that Lana puts her left leg onto the bridge into a sitting position. They then cut to a different angle but now both her legs are still dangling and she eventually puts her right leg on the bridge first.
Continuity mistake: As Lionel says "Good morning, Miss Sullivan." there is a camera change from Chloe's left to her right. When the camera is on the left, her left arm is down. When the camera jumps to her right her left arm is now in the middle of placing something high up on the layout board she is using.
Revealing mistake: As Tyler slides across the floor, after Clark knocks him out of Whitney's father's room, he hits the camera. When he does the camera has a noticeable shake to it because of it.
Continuity mistake: The field trip is supposed to be on the 39th floor, as stated by Clark and the sign next to the elevator. The view outside the large windows as Lionel is talking shows that they are no more than 5 stories up.
Continuity mistake: Clark and Martha show up at the barn. The interior rear view mirror is missing when looking out from inside the car, but it is there when looking in the car from outside.
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