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.
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.
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)
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.
Continuity mistake: When Jonathan goes to talk to Desiree, Jonathan throws Desiree a bathrobe. She then proceeds to put it on and lifts her right hand over her head as she does so. Cut to a different angle and now she is raising her right hand over her head once again.
Continuity mistake: Byron mom buys him a book by Edgar Allan Poe at the used bookstore. Byron takes it with his right hand and looks at it. Cut to a wider angle (as Byron stands up) but now he is holding the book in his left hand.
Continuity mistake: When Dr. Hamilton was about to pour liquid kryptonite on Clark, Pete hits him on the back and he goes crashing onto a table knocking everything on it off the table. Yet later we see an open bottle of liquid kryptonite on the edge of the table (which was cleared by the doctor earlier) dripping onto the doctors forehead.
Continuity mistake: At the collision, Pete looks out over the cornfield and sees the flashing turn signal of the truck but not its headlights, which should be brighter. (00:03:20)
Skinwalker - S2-E10
Continuity mistake: When Lex is talking to Lionel outside the building site at the end, Lex's sunglasses disappear while the camera is on Lionel and reappear when back on Lex. This happens after Lionel turns to face slightly behind Lex and continues throughout the rest of that exchange.
Continuity mistake: After Jonathan and Martha talk about Clark's new behavior in the porch, we see Lana at the Talon sprinkling something onto a drink. When Clark was still walking towards Lana we can see that the pointed part of the container Lana was holding was pointing up. Cut to a different angle and now the pointed part of the container Lana is holding is pointing down.
Continuity mistake: After Clark says "I'm not leaving." Jonathan starts to talk about the list of things Martha needed to get done. As Jonathan says this there is a camera switch. Before the switch Clark is next to the window turned toward his dad. After the switch Clark is now standing further back from the window behind Jonathan's right shoulder.
Exodus (2) - S2-E23
Continuity mistake: As Jor-El is first burning the mark on Clark's chest the mark moves to the upper right part of his chest. In the next shot, closer in on Clark, you can see the same area again but now there is no mark where there was one before.
Continuity mistake: Lex brings some comic books to Ryan at the hospital. He holds all of them with his left hand. He then shows 66 of the comic to Ryan and holds it with both hands. Cut to a different angle and now he is holding the comics with just his left hand once again.
Continuity mistake: Lionel press conference about Lex's kidnapping only infuriates Rachel. She then picks up an axe and was about to swing at the tied up Lex when he manages to get his right leg free and kick Rachel backwards. As she falls backwards, we can see that she drops the axe off to her left side. Cut to a different angle but now the axe is over her head to her right side.
Continuity mistake: While in the line to claim their class rings, Pete holds a folded piece of paper (probably his receipt). As Clark says: "I earned that money.", Pete starts to unfold the paper. Cut to a different angle as Clark continues: "Besides, my dad said." but now Pete is looking at a completely unfolded piece of paper.
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