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.
Continuity mistake: When Lex is talking to Lionel outside the building site at the end, Lex's sunglasses disappear while the camera is on Lionel and reappear when back on Lex. This happens after Lionel turns to face slightly behind Lex and continues throughout the rest of that exchange.
Continuity mistake: As Clark walks into his grandfather's motel room, his hands are behind his back. He turns to face his grandfather and both hands are now in front of him holding the photo album. The next shot shows him in the foreground raising his left arm from his side to hold the album.
Deliberate mistake: Clark's CPR form is terrible. When he performs emergency breaths on Lex, Lex's chest doesn't rise and fall, indicating that he's not actually breathing much air in. He doesn't bother to measure for the proper location for chest compressions, a very important step that is the difference between proper CPR and simply cracking ribs. As he performs compressions, he is not chanting the rhythm (one-and-two-and-three) and his elbows are bent. All of these were altered for dramatic reasons or the purpose of safety, but the sloppy technique probably would have killed Lex.
Plot hole: In the episode Onyx, Lex's alter ego holds him hostage in the wine cellar claiming that when they were kids, Lex accidentally got locked in down there. In the pilot episode, it is established that although Lionel had the castle shipped over from Scotland brick by brick and built, they never moved into it.
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.
Continuity mistake: At the beginning of the episode an announcer calls Jonathan's name and he appears almost immediately. Later on we see what happens backstage and when we hear the announcer call Jonathan's name. The second time through he has time to say a few last words with Lois, go to the edge of the curtain and take a breath before he steps out on stage. The timing of the two scenes don't match.