Continuity mistake: When Chloe is kissing Justin the shot is behind him and her hands are not on his neck. The shot switches to behind Chloe and she does have her hands on his neck.
Revealing mistake: When the gas pipe explodes at the beginning before the credits, the camera goes to an aerial view. You can see that the explosion started from behind the gas pipes. (00:01:50)
Continuity mistake: As Chloe leaves Clark calls out her name. In the shot from Chloe's side of the room, Clark is holding the pitchfork horizontally low in front of him. The shot switches, as Chloe finishes her turn, and now Clark is holding the pitchfork with his arm bent so that the pitchfork is no longer low in front of his waist.
Tempest (1) - S1-E21
Continuity mistake: The way the pillar is on top of Lionel changes in the scene. In the first shot, he's on his side and it lands on his hip. In the next shot he's now on his back and the pillar is going somewhat across his body. In the wide shot of him as the roof falls, the pillar is below his belt, almost perpendicular to his body. Then back to being on his stomach and part of his chest.
Vortex (2) - S2-E1
Continuity mistake: When Clark and Lex are searching for Clark's dad, right after Clark gets mad at Lex and leaves it shows a head shot of Lex with the bandage over his left eye. In the beginning of the show he was injured over his right eye. (00:15:30)
Vortex (2) - S2-E1
Continuity mistake: Nixon raises the bar to kill Jonathan with a ridged side up, but when he is shot he is holding the smooth side up. (00:32:00)
Vortex (2) - S2-E1
Continuity mistake: When Martha Kent and Lana were talking about the meteor shower in the Talon Relief Center they sit down on the stairs. Lana puts both her hands on her knees. But in the next shot now her arms are outstretched in front of her, and now it's her elbows which are on her knees.
Vortex (2) - S2-E1
Plot hole: When Nixon and Jonathan are trapped in the crypt after the landslide, Nixon says he can't breathe, and Jonathan says this is because the landslide cut off the air supply. However, we can see beams of sunlight shining in. So, unless the ceiling of the crypt is made of airtight glass, that landslide didn't cut off the entire air supply.
Vortex (2) - S2-E1
Audio problem: When Lex talks to Clark, Clark clicks his flashlight on, and you hear the click signifying he has turned it on. But in the next shot, the flashlight is now off, without another click sound heard to signify that the flashlight was turned off.
Vortex (2) - S2-E1
Continuity mistake: When Clark, Pete and Chloe were looking for Clark's father in the woods, Pete says: 'the twister must have dropped it here' and we see Chloe holding the map in her right hand. Cut to a different angle (as Clark runs towards the screen) and in the background we see Chloe holding the map with her left hand instead.
Vortex (2) - S2-E1
Continuity mistake: When Clark brings Lana to the hospital, a doctor attends to her and checks her vitals. In a close up we see the doctors right hand on Lana's neck checking her pulse and her left hand is no where in sight. Cut to a wider angle (as Clark runs away) but now the doctor is holding a flashlight in her right hand and her left hand is on Lana's forehead.
Vortex (2) - S2-E1
Continuity mistake: When Clark, Pete and Chloe were searching for Clark's father in the woods, they stumble upon a motor home dropped by the tornado. Chloe then picks up a Nixon's camera and looks at it. Cut to Nixon and Jonathan Kent then back to a wide shot as we see Chloe throwing the camera down onto the ground. Clark then uses his X-Ray vision once again. Cut back to a wider angle (as they walk away) yet we see Chloe throw down the camera once again.
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?
Continuity mistake: After Lex confronts Desiree about changing her name, Lex says 'we really need to discuss this' Desiree then kisses Lex and they both tilt their heads to their left. Cut to a different angle and they are both tilting her heads to the right.
Continuity mistake: When Lana was making a video to send to Whitney, we see her interviewing Clark. We first see Clark through the camera's view finder. Lana then drops the camera (pointing it down) such that we see Clark's feet. Cut to a different angle but now Lana's is pointing the camera at Clark's chest level.
Continuity mistake: When Desiree walks into Clark's barn to work on their 'student-teacher relations', she holds her hair up with her right hand as she complains about the heat. She then lets her hair down and fixes it. Cut to a different angle and she is letting her hair down once again.
Continuity mistake: In Jail, when the sheriff tells Chloe and Lana that visiting time is over, we see Clark holding the bars with his left hand as he tells the girls that his dad went to see Desiree. Cut to a different angle (from inside the jail cell) but now Clark is no longer holding onto the bars and only holds them a few seconds later.
Continuity mistake: When Clark decides to stay home from school because he cannot control his heat vision, his father decides to have a talk with him. Jonathan pulls his son to face him and them places both his hands on Clark's shoulders. Cut to a different angle as Jonathan says: 'Clark, look at me ' but now we see his left hand on Clark's neck. Cut back to the previous angle and his hands are on Clark's shoulders again.
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