Continuity mistake: When Jonathan lectures Clark about the danger of accepting gifts from Luthors, the key he twirls is a GM truck key, not a Ford truck key.
Continuity mistake: After the meteor shower, the bit of hair that Mr. Luthor finds in the cornfield changes in his hands from stretched straight to curled. (00:06:15)
Continuity mistake: The hole in the guard rail changes size and shape between the shot of Lex driving off it and another looking up at it from below. (00:18:10)
Continuity mistake: Season 7, episode "Persona". When Lana walks in from the balcony her hair swaps from being in front of her shoulder to behind it, then back again. Then when she sees Bizzaro's face in the reflection of the glass, her hair is styled differently again.
Continuity mistake: In the truck right before the parade passes them by, Jonathan Kent kisses his wife. Cut to a different angle but this time his left hand is on her cheek. It wasn't there in the prior angle. (00:02:15)
Continuity mistake: After Greg hits Clark with the pipe in the foundry, Clark's hands are very dirty. In the closeup on Clark's hand immediately after he lands, the hand is clean to show the effects of the Kryptonite. (00:39:45)
Continuity mistake: As Chloe hurries to put Justin's art book back before Justin comes in there is a piece of white paper sticking out of the top and bottom, based on the way she put it back, of the folder. When Justin sees the folder has been moved there are no papers sticking out.
Continuity mistake: As Clark jumps the fence, to stop Jonathan from falling, you can see Martha is standing in sunshine with the shadow of the barn well away from her. When Clark actually catches Jonathan suddenly Martha is standing in the shadow of the barn.
Continuity mistake: Despite the fact that Clark and Jonathan are looking in the rafters above them for Greg, their flashlights stay relatively level. (00:26:35)
Continuity mistake: When Lex is about to hit Clark with his car, Clark alternates between facing the car and facing the bridge. (00:17:20)
Continuity mistake: Just before the final play of the game starts there is a shot of the scoreboard. The scoreboard reads 4th and 10 (yards) with 10 seconds to go. The announcer then says it is 4th and 1 with 10 seconds to go.
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.
Continuity mistake: When Chloe shows the newspaper to Jimmy with his photo on it. The photo is not the same when it is shown in the close-up.
Continuity mistake: When Lewis says to Lex ".the bitch that set you up." he is holding the stick with the point in his wrist. In the very next shot he is gripping the stick by the side and not from the point.
Continuity mistake: As Clark walks up to Lex you can see the tip of Lex's cue stick is 3-4 inches away from the rail. Before Clark picks it up the stick is now right up against the rail.
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