Continuity mistake: After Lois pins the sketch of the Green Arrow, the pushpin changes position. In some shots, it's across the top of the paper and in others it's in between the top of the sketch and top of the paper.
Factual error: Chloe wants to access the security camera files on the Luthor mansion server to see what happened to Lex. She can't crack the password, so she says she'll just download the entire hard drive. She pulls out a thumb drive and proceeds to do so. Two big technical problems here. Firstly, if she can't log in, she can't access anything on the server. And Secondly, the entire hard drive for a server (which is huge) containing video files (which are huge) will not fit on any thumb drive.
Other mistake: Lex picks up a chisel and stabs Clark in the side. It bounces off and out of Lex's hand. The last couple inches are bent and twisted. Chisels are made from extremely tough steel. But no matter how hard Clark is, Lex is not strong enough to exert the force necessary to bend the chisel itself.
Other mistake: The bowling scorecard for Chloe and Lana is wrong. It shows Chloe knocking down 1 pin (-|1) in the first frame but getting 3 points, then a spare in the 2nd frame but only getting 1 point. The math is wrong until the 7th frame where is ends up showing the correct score. Lana's score is correct, except on frame 9 it shows she knocked over 6 pins on her first ball and is on her 2nd ball, but when it cuts to her, all 10 pins are up. Plus an unfinished 9th frame shouldn't show a score.
Factual error: Lana is trying to find out what Lex is up to. She gets a hold of his briefcase and takes it to the mansion where she shoots the locks off the case. When she does the case jumps a little bit but this is far less than it should. She is shooting at it from less than a foot away. The force of the bullet should have sent that case sliding across the desk at that range. (00:15:35)
Plot hole: Clark is crippled throughout much of the episode due to there being kryptonite in the tunnels. At one point he gets a rock stuck in his arm and he bleeds from this wound. For much of the time after this he has blood running down his arm from this wound. After he gets out of the tunnel he is healed but the problem is the blood from the wound also disappears. The actual wound should have healed up but the blood from that wound should still be shown staining his arm.
Continuity mistake: Lana was found shot in her upper left shoulder but at the end of the show she has a sling on her right arm. (00:42:00 - 00:43:05)
Continuity mistake: When Chloe and Jimmy find Lana shot in the elevator, there is a gun on the floor beside her, with a small pool of blood beside in the gun. In the next closeup shot on the floor, the small pool of blood is gone. (00:42:00)
Audio problem: When Jimmy is in the 1940s Talon we can hear the sound of a saxophone in the number before Lois arrives. Nevertheless, as we can see on the stage, there are only three instrument: a drum, a piano, and a bass. (00:52:00)
Audio problem: When Noir-Lois comes out to sing, the microphone picks up her voice before she's anywhere close enough for it to do so. (00:52:30)
Continuity mistake: When Lana hands the gun to Jimmy, she hands it to him aimed away from her. When Jimmy takes it, it is aimed towards her. (00:59:00)
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: At the beginning of the episode, we see that the clock reads 2 o'clock. Jimmy then takes Chloe into the back room to his set-up movie date. A little into the scene, they then hear a gunshot. When they rush out, the clock now reads 4:15. However Chloe and Jimmy were not in the back room for this long. At 4:15 they find Lana shot, and call 911. Then after the credits, we return to the scene, but now the police have arrived. But now the clock reads 2:15. There is no way the police would have taken so long, that the clock would have jumped all the way around from 4:15 to 2:15, therefore the continuity on this clock is mixed up.
Other mistake: When Jimmy wakes up in 1940, on his desk calendar it's Saturday the 3rd. The newspaper says it's May 3rd, 1940, but that was a Friday.
Continuity mistake: When Lionel is watching the video and drawing Kryptonian symbols, some of the symbols change in between shots. For example, when he draws "minion" one of the dots is touching the square. When he writes the word, everything is nice and neat and the dots aren't touching anything.
Continuity mistake: When Clark looks at Phillipe's police report, there is a photo of Phillipe facing sideways. In the next shot the photo has changed, so that now he is facing forward. (02:21:10)
Continuity mistake: When Lois attack the guard down in the dam, she hits his face, which causes the black cap that the guard is wearing to begin to fall off. Yet in the next shot the hat is firmly back on his head, before it is completely knocked off by Lois' next hit. (02:23:00)
Continuity mistake: When Chloe finds Lois stabbed in the dam, we see Lois on the floor with her arm hanging so that her hand is right beside the stab wound. However in the next close up of the wound, her hand isn't there. It's back beside it in the next shot. (02:28:20)
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