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.
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.
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.
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.
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.