Continuity mistake: Jason Teague arrives at the Kent farm. He fires a shot into the windshield of the Kent's truck. So we obviously know the gun is loaded. Later, inside the Kent's house, Jason still has Jonathan and Martha held hostage. After Jason mentions the symbols burned into the field Martha says she doesn't know what he is talking about. Jason gets upset and racks the shotgun but when he does no shotgun shell, used or unused, is ejected. Now Jason would have had to keep the gun loaded while moving Jonathan and Martha back to the house as he would have had no time to unload and reload his gun.
Continuity mistake: When Clark is in the barn throwing footballs through the tire. He starts out with four footballs on the rack, but after he throws two, there's only one ball left.
Revealing mistake: When Lana has her nightmare, she wakes up in a room and discovers various people on pedestals, underneath body sheets. During the scene, some of the people under the sheets can be seen lightly breathing, although everyone under them is dead.
Transference - S4-E6
Continuity mistake: Martha visits Lionel in prison not knowing Lionel is actually Clark. As she says "I'm only here because you told me it had to do with the safety of my son." the camera changes. Between changes, as Martha says "you", her left hand goes from being under the table to instantly being on top of the table.
Other mistake: When Clark is in the girl's room and a noise comes from the closet, Clark uses his X-Ray vision to see there's a person in there because he can see the skeleton and is surprised to see it's Lois when he opens the door. However, it's been shown before that Clark can use his X-Ray vision to see objects and people through solid objects. He should have been able to see that it was Lois rather than just a skeleton of an unknown person.
Factual error: When Lionel is leaving the prison, there is a bus unloading convicts as he walks past. No prison in the world would ever unload inmates and release an inmate in the same area at the same time.
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