Continuity mistake: The raindrops on Clark's shirt disappear and reappear between shots. Clark's shirt is dry when he turns to Chloe and asks "I'm not normal?" but before and after this his shirt has raindrops on it. This happens again a few moments later as Lois starts to talk about "panicking in times of crisis", Clark turns towards Lois and his shirt is dry.
Other mistake: When Clark confronts Jason Dante and tells him the race is off, one of Dante's thug friends picks up the krptonite/nitrous oxide booster tank and only then does Clark start feeling the effects of the kryptonite. Even though the tank had been sitting out uncovered well before the guy picked it up.
Continuity mistake: When Seth is testing his powers in the hospital room he tries to move a cart at the foot of his bed. To do this he has to raise his hand to use the magnetic power he has. In shots from the front his right hand is palm down using his power but when the shot switches to behind Seth, to show the cart starting to move, his palm is now turned towards his left. His hand is back to being palm down when the shot switches back to the front.
Factual error: When Ian throws the unconscious Chloe over the edge of the dam we see her falling down as Clark falls with her. However, Chloe's body position is unnatural for someone who is falling while unconscious. Her head/body is arched backwards when air resistance should have forced her body to become level/straight.
Continuity mistake: When Lex tells Clark about Lionel finding the wire, Clark moves over to Lex and says that finding something incriminating on Lionel shouldn't be too difficult. Between shots, Lex and Clark's positions change in relation to each other.
Continuity mistake: Clark arrives at the Talon after Lex reads the mysterious love letter for Lana. Lex the gives back the letter to Lana twice between shots.
Audio problem: After they get the spaceship into Pete's shed, Pete wants to go tell Chloe. Clark insists that he doesn't and Pete says "To her, this thing is the Holy Grail.". The shot zooms in and Pete's mouth shows him saying "Holy Grail" again even though he already said it and you don't hear the words.
Continuity mistake: Clark tries to talk to Pete into helping him find his ship. As Clark was talking about the driver, we see the cover to Pete's locker in the foreground. Cut to a different angle and now Pete's left hand is on the locker and it wasn't there in the previous angle.
Continuity mistake: When Clark looks over to Lana, while in the coach's office, she starts to pull up her right sleeve that had slipped down. As Clark says "Lana.what are you doing here?" the shot is behind Lana and her sleeve is down and is showing a lot of her upper arm and shoulder but when the shot switches back to the front of Lana, she has her sleeve pulled up covering most of her upper arm.
Audio problem: When the thief with one arm tells his other two buddies to "check this out" the shot switches to the right side of him. In that shot you can see this guy say "check this out" again.
Exodus (2) - S2-E23
Continuity mistake: When Kent leaves on his motorbike at the end of the episode, in a shot from behind Lana crosses her arms. In the next closeup her right arm is up by her mouth.
Continuity mistake: The motorcyclist has his visor down when he appears at the end of the alley. He raises the gun, then reaches up and lowers his visor again. (00:27:00)
Audio problem: While Sean and Whitney are tossing the football at the lake edge, at one point we hear Whitney catch the ball offscreen while the camera is on Sean. The camera then cuts back to Whitney and he catches the ball on screen. (00:03:20)
Continuity mistake: When Chloe and Lois return to where the barn door landed, the shadows and sunshine keep changing between shots. (00:55:35)
Continuity mistake: At the beginning of the episode an announcer calls Jonathan's name and he appears almost immediately. Later on we see what happens backstage and when we hear the announcer call Jonathan's name. The second time through he has time to say a few last words with Lois, go to the edge of the curtain and take a breath before he steps out on stage. The timing of the two scenes don't match.
Continuity mistake: The blood on Lana's face is different then how it was in the previous episode. While at the crater in Commencement she has two distinct lines of blood on her face. One on her left cheek is thick and the one on the right cheek goes down past her lips. While at the crater in this episode the left line is then while the right line is shorter. These two scenes should be identical since Arrival picks up right after Commencement.
Phoenix (2) - S3-E2
Continuity mistake: When Lex pulls the gun on Linoel, when the camera is on Lex he is pointing the gun in Lionel's face. When the camera is on Lionel, Lex is pointing the gun in Lionel's chest.
Continuity mistake: When Jonathan goes to talk to Desiree, we see her getting out of the swimming pool. However her hair is just damp when it should have been completely wet and dripping all over the place considering the length of her hair.
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