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.
Continuity mistake: Lex's aide is shot in the back as he makes a run for the door. When he goes down he slides head first almost all the way to the door. A few moments later, just as Flynn shoots out the security camera, in the security monitor image Lex's aide is now in a different position.
Continuity mistake: Jonathan reveals the kryptonite to Clark/Dawn and Clark starts to react to it. Because of the kryptonite Clark drops the tiara he took from Chloe and it hits the floor near Chloe's hand. Then, just before Dawn is forced out of Clark's body, the tiara has slid several feet away and is now close to the furnace. Clark turns his attention to Chloe, she is faking an injury at this point, but now the tiara has moved back to be near her hand.
Continuity mistake: In the barn loft evil Lex has a kryptonite ring in a lead box. When the camera is in front of Lex he is holding the box so that the lid is pointed towards his thumb. When the camera is behind Lex the box is turned so that the lid is pointed towards the end of his fingers.
Continuity mistake: As Clark and Geoff are driving, the first shot of the SUV as it comes around the corner shows the ground is wet and the wipers are going. During their conversation the windows are constantly being rained on. Geoff points to the stadium and they arrive a few minutes later and as they drive into the garage you can see the street is dry.
Audio problem: Clark is upset over the death of Alicia and is in the barn loft bouncing a ball off the wall. His parents come up and Jonathan sits next to him and tells him that what happened was not Clark's fault. The very next shot shows Martha sitting down and you hear Clark throw the ball again but you can see that his hands never make and motion to correspond with that action.
Continuity mistake: As Lana says "I was thinking the same thing but we don't seem to be very good at it." there is a camera change as she says "but". Before the change she only has the red cup on the tray but after the change, even though she didn't pick it up, she has a red and a yellow cup on the tray. The other cup was on the table and jumps to the tray between shots.
Plot hole: During Clark's rescuing Lana from the fire in the basement, Clark wakes Lana just before he is grabbed by the coach. Clark then tosses the coach all the way across the room and into a wall. Lana makes no mention of how Clark could toss a full grown man across a room like that even though it happens right in front of her face.
Continuity mistake: After Dante says "...if you want to turn that tortoise into a hare just give me a call." he walks off and the shot follows him as he walks all the way over to a black car and starts to work on it. The shot returns to Clark and Pete and Dante is shown walking away again on the left side of the screen.