Continuity mistake: In the head on shot of the car that almost hits Mr. Altman you see the driver of that car react by turning his car to the left. In the very next shot, as Clark and Mr. Altman are just coming to a stop after Clark's high speed rescue, the driver is now turning his car to the right, as shown by which way his wheels are turned.
Continuity mistake: After Lionel finds out about the wire that Lex has been wearing, he sits down and tells Lex to get out. As Lex leaves, in the wide shot, Lionel drops his hands down to his lap. In the zoomed in shot Lionel's hands are up to his face as he plays with the wire. There was no time for him to make that move between shots.
Continuity mistake: Lionel press conference about Lex's kidnapping only infuriates Rachel. She then picks up an axe and was about to swing at the tied up Lex when he manages to get his right leg free and kick Rachel backwards. As she falls backwards, we can see that she drops the axe off to her left side. Cut to a different angle but now the axe is over her head to her right side.
Continuity mistake: While in the line to claim their class rings, Pete holds a folded piece of paper (probably his receipt). As Clark says: "I earned that money.", Pete starts to unfold the paper. Cut to a different angle as Clark continues: "Besides, my dad said." but now Pete is looking at a completely unfolded piece of paper.
Continuity mistake: The raindrops on Clark's shirt disappear and reappear between shots. Clark's shirt is dry when he turns to Chloe and asks "I'm not normal?" but before and after this his shirt has raindrops on it. This happens again a few moments later as Lois starts to talk about "panicking in times of crisis", Clark turns towards Lois and his shirt is dry.
Continuity mistake: As Clark is sitting in his barn's loft his mother enters while he watches a model of the solar system. In the shot when he turns it off the large red globe, which looks to be Jupiter, stops well to the right of the model's sun in this shot. When the shot returns to Clark, Jupiter is now partially in front of the sun. Clark had not moved his hand from the off switch so he didn't move the model by hand and the model would have taken longer to make another rotation to put in that position.
Plot hole: When Clark confronts Jason Dante and tells him the race is off, one of Dante's thug friends picks up the krptonite/nitrous oxide booster tank and only then does Clark start feeling the effects of the kryptonite. Even though the tank had been sitting out uncovered well before the guy picked it up.
Continuity mistake: When Seth is testing his powers in the hospital room he tries to move a cart at the foot of his bed. To do this he has to raise his hand to use the magnetic power he has. In shots from the front his right hand is palm down using his power but when the shot switches to behind Seth, to show the cart starting to move, his palm is now turned towards his left. His hand is back to being palm down when the shot switches back to the front.
Revealing mistake: Clark uses his heat vision to warm up Alicia's cup of hot chocolate. When the drink is hot enough to start giving off steam, the "steam" is not water vapor. Water vapor would be nearly clear and rise straight up from the cup. This "steam" is more likely from a piece of dry ice as the vapor is rolling over the side.
Continuity mistake: When Lex first tries to break out of Belle Reve, he stabs a security guard in the leg with a pencil deep enough to draw a large amount of blood on the guy's pants leg. But when Lex is trying to incapacitate the man you can see the pencil flopping around on the guards leg and not sticking inside the guy's leg.
Audio problem: In the scene where Jason and Isabelle/Lana are talking and he is about to burn the book with the lighter, she quickly grabs the book with her magic. Isabelle then says some sort of spell flinging Jason against the wall to the right. In the shot where you see him thrown against the wall, Isabelle has already said the spell, but you can see her mouth moving saying the same thing (though nothing is heard).