Continuity mistake: Chloe makes an $80 bet with Mxyzptlk at the beginning of the episode. When he pays her in the Torch office, he peels off seven 20-dollar bills for a total of $140 instead of the $160 it should be. (00:09:00)
Continuity mistake: Jason accesses Lex's computer and Lex catches him. After a discussion on an email Jason found Lex says "Burying ladies in the backyard isn't exactly a hobby of mine, Jason." Lex then just stands there staring at Jason. During their stare down the camera jumps back behind Lex and then back to behind Jason. During these camera changes the lighting on the left side of Lex's face changes. When the camera is behind Jason, Lex's left side is dark. When the cameras is behind Lex, Lex's left side is lit up.
Continuity mistake: While Martha reads to Jonathan, as he is in a coma, the light on his hands change. In the shot from the right side of Jonathan's bed his hands have only a normal level of light like from a small table lamp. The shot changes to look at Jonathan from the doctor's point of view and suddenly Jonathan's hands are very brightly lit like from a spotlight. No one changed or turned on any other lights between shots.
Continuity mistake: As Lana saves Lois from Trent, as Lana first starts to spray the pepper spray/mace the camera is behind Trent and the mace is coming out in a mist. The camera jumps to behind Lana and now the mace is firing in a steady stream.
Continuity mistake: When Bad Lex is beating up Good Lex in the cellar right before their bodies are joined again, he repeatedly hits him on the right side of his face. However, when the two are finally fused back together, there is a bruising on the left side of Lex's face.
Continuity mistake: In the CG shot of the shotgun shot flying in slow motion towards the camera, the blue florescent light that was swinging in the previous shots is gone.
Continuity mistake: As Clark says "Eve Andrews was wearing two earrings when she died," during the line there is a camera change. Before the change Lionel has both arms on the table, but after the change he has one arm up examining the earring.
Continuity mistake: When the mirror falls on Lana and shatters on her, you can see that there are bleeding cuts on the left side of her face. However, for the rest of the episode, there are no cuts on the left side of the face (where they should be) but there are cuts on the right side of her face.
Suggested correction: When the mirror falls, we only see her left side. But in the hospital you can plainly see both cheeks were cut up, the right one a bit more. Throughout the episode though, the cuts on the left side never disappear and there just seems to be more shots of her right side when she's out of the hospital.
Continuity mistake: Before Clark throws the two bad guys against the side of the barn there is no snow falling at this point. When the shot switches to Krypto saving Hercules you can see that now it is snowing rather heavily. This is far too fast to happen naturally.
Continuity mistake: As Lois and Clark talk about her leaving, Clark turns to talk to her. Before he turns around the shoulder protector is between his hand and his shoulder and the red side is facing out. In the next shot, even though he made no motion to alter the position, it is now fully on his shoulder with the black side facing out.
Continuity mistake: Jason Teague arrives at the Kent farm. He fires a shot into the windshield of the Kent's truck. So we obviously know the gun is loaded. Later, inside the Kent's house, Jason still has Jonathan and Martha held hostage. After Jason mentions the symbols burned into the field Martha says she doesn't know what he is talking about. Jason gets upset and racks the shotgun but when he does no shotgun shell, used or unused, is ejected. Now Jason would have had to keep the gun loaded while moving Jonathan and Martha back to the house as he would have had no time to unload and reload his gun.
Continuity mistake: When Clark is in the barn throwing footballs through the tire. He starts out with four footballs on the rack, but after he throws two, there's only one ball left.
Transference - S4-E6
Continuity mistake: Martha visits Lionel in prison not knowing Lionel is actually Clark. As she says "I'm only here because you told me it had to do with the safety of my son." the camera changes. Between changes, as Martha says "you", her left hand goes from being under the table to instantly being on top of the table.