Other mistake: Lois digs up Chloe's grave site to unearth her casket. It is obvious that the casket is not buried six feet deep. You would think, with all that is going on, that LuthorCorp would have at least buried the casket deeper to deter inquisitive eyes and maybe throw in a few scattered bones for good measure.
Plot hole: In episode 4-16: "Lucy," there is no reason for the criminals to be chasing Lucy on the ski slopes at the beginning of the episode. We learn later that she's been working with them all along; she calls Lois during the chase, and the call is part of Lucy's plan with the criminals. Lucy being chased by the criminals would make sense given the story she gives Clark during the next part of the episode, but it doesn't make sense for what we ultimately learn is the truth. And nobody from Smallville is anywhere near the ski chase, so it also doesn't make sense as any kind of a ruse.
Plot hole: During the flashback scene showing how Chloe and her father survive the house explosion it is explained that there was a team in the house and they grab Chloe and her father and rush them into a tunnel just seconds before the house explodes. However, as seen in the episode Covenant, Chloe is standing next to the door and Chloe's father is more than 15 feet away from her when the door of the house shuts. As soon as that door shuts the house explodes so unless this S.W.A.T. has Clark's super speed ability this would be very much impossible.
Continuity mistake: As Trent and Lionel talk, while Lionel is in the hospital bed, when the camera is behind Trent his shoulder and neck are barely illuminated and is in shadow as the camera is looking down on Lionel. When the camera is looking up at Trent, even though he has not moved, his shoulder and neck are now brightly lit and shows no sign of a shadow.
Continuity mistake: As Lana and Lex are talking, as Lana says "Actually, umm, I came by because.". In the middle of her going "umm" there is a camera change. Before the change Lana has her right hand on the arm of the seat. After the change she now has her right hand scratching her head.
Continuity mistake: After Clark gives Chloe the piece of paper with the list of cars that checked into the hotel, Chloe holds the paper in front of a folded up newspaper. Between shots, the newspaper turns the direction it faces. Then in the next shot, Chloe is only holding the piece of paper, and the newspaper that she was holding behind it has now disappeared.
Continuity mistake: When Clark first finds the necklace in the shower drain it is all in a single line with no loops or overlaps except at the very end. As Clark picks the necklace up it now has several loops and overlaps all along the chain and not just at the end where the clasp is.