Continuity mistake: When Lucas is in the Luthor mansion talking to Lionel and Lex, he picks up and inspects the samurai sword, then returns it to the holder, hanging it on one peg by the strap. In the next immediate shot, it is resting between the pegs, as it was before he picked it up.
Continuity mistake: The position of Clark's sleeve to the tourniquet change between shots. When Dr. Bryce first ties the tourniquet she does so at about an inch from the end of the sleeve. In the next shot, as Clark lies unconscious and nobody touches his sleeve, the tourniquet is tied around the sleeve and no longer on his skin. Just before Dr. Bryce sticks the needle in it's back to being an inch from his sleeve.
Continuity mistake: Just before Dr. Bryce removes the vial she unties the tourniquet and the straps are completely off of Clark's arm. In the shot of Clark after that, as Dr. Bryce looks at the vial, she unties the tourniquet again.
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.
Audio problem: After the DCA shows Clark and Jonathan the metallic key, Clark says, "We need to think about mom," but his lips are not moving.
Continuity mistake: In the kitchen, Martha collapses and Clark catches her just in time. Jonathan then rushes to his wife and puts his right hand on her cheek and his left hand on Clark's shoulder. Cut to a close up of Martha as Jonathan calls her name but now he has both his hands on Martha's face.
Continuity mistake: When Martha is in the kitchen and starts having a coughing fit from the toxin, she drops the pitcher of lemonade. The pitcher lands on its side and breaks, but in the next shot, the broken base is positioned upright, sitting level on the floor, the jagged broken edges waiting to impale Martha.
Audio problem: After Clark is dumped into the blast furnace and the thieves make a getaway in their truck, you can hear the sound of an accelerating engine as it's driving away, but the brake lights are on.
Revealing mistake: Clark tries to stop the three guys who are inhaling refined kryptonite. As Clark gets tossed through a window, you can see the explosion of a small charge in the bottom left of the widow. Highly noticeable since Clark hits nowhere near where this charge goes off.
Exodus (2) - S2-E23
Continuity mistake: When Clark is fighting with Dr. Walden, twice Dr. Walden sends Clark flying, with his powers. Both times, when Clark hits the ground, he becomes quite buried into the soft dirt, not entirely, but relatively sunken into it. However when it will cut to the next shot, Clark is lying on the dirt without being buried into it at all. This is obviously due to switches between actor and stunt double.
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.
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.
Exodus (2) - S2-E23
Audio problem: At the wedding, after Jonathon gives Lex the compass, in a side shot we hear Jonathon say a line, yet his mouth is completely out of sync.
Other mistake: Early in the episode, Clark uses his heat vision to blow up a police car. In the shot where we see the policewoman diving for cover, there is a front view of the car as it is exploding. The license plate on the front of the car IS a Metropolis plate, however, as the plate falls off, the white placard that auto companies and dealerships place in the license plate frames on new vehicles before they are registered and which are removed once plates are installed is visible. (00:07:10)
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: When Chloe and Lionel finish their discussion in the cave the shot focuses on the Naman/Segeth glyph and focuses through the glyph to a transition shot of an island that Lex is on. When we first see this island it is flat and covered with trees. The next time the island is shown there is now a large volcano/mountain that was not their when we first see the island.
Phoenix (2) - S3-E2
Plot hole: When Edge needs the vial of Clark's blood back, Edge holds Clark's parents hostage. Clark decides to use a sharp piece of kryptonite rock to cut his skin and give Edge a new sample. When Clark picks it up, and when he places the kryptonite rock on his skin, he shows no sign of the usual effects of the rock which include the green lines radiating up his arms.
Phoenix (2) - S3-E2
Continuity mistake: As Morgan Edge hands Lionel the bag with the mason jar of blood the camera is on Lionel's side and bag has a very neatly folded flap to keep the top closed. As Lionel takes the bag, while the camera is on Edge's side, the opening is wrinkled and not folded shut as it was before.
Phoenix (2) - S3-E2
Continuity mistake: When Clark and Jonathan return home, Jonathan collapses on the couch. It shows Clark rushing to his side. But in the next shot where it shows Martha's reaction, you can see Clark rushing to his side 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