Continuity mistake: During the flashback that happens at the Luthor mansion, the one that starts with the cup shattering on the floor, young Lex is shown peeking through a slightly cracked open door. Just after Lionel asks the nanny to give him Julian there is a shot of Lex peeking in and you can see that he has hair on his forehead. Now Lex, at this point, would have been bald, as a result of the meteor shower in Smallville for several years and would have no hair at all on his head in this flashback. In fact when Lionel finally realizes that Lex is outside the door we see that Lex has no hair on his head.
Suggested correction: Lex is bald but still has eyebrows. There's never a shot of young Lex with hair on his head. You never even see his head when he's peeking, but you do see the hair from his eyebrows.
Continuity mistake: The first time Seth tries levitating a spoon, he floats it a few inches towards him. When Lana enters and breaks his concentration, it falls back down almost exactly where it had been.
Suggested correction: Even though it's impossible to tell how much the spoon moves towards him, the spoon was in the middle of the jello, then lands in front of the jello, a few inches away from the middle.
Factual error: Tate fires at Clark, who is dressed as the drifter, 8-9 times from a revolver that is chambered for only 6 rounds.
Suggested correction: I count 5 shots fired, which is how he had 1 left that he was planning on using on himself. You must be counting ricochets or other sounds as shots fired.
Visible crew/equipment: When Lex and Chloe are talking after the morgue, you can see a crewmember passing behind her at 30:53. (00:30:53)
Suggested correction: You see a person walk behind her in a corridor. Since it is very obvious and occurs during a short cut where nothing else is happening, it is deliberate. A fundamental rule on film sets is that once "action" is called, no-one moves if they don't have to. If a crew member had walked through the shot like that, they would have done a new take or just use a different segment of the shot.