Visible crew/equipment: Episode 22, Season 5 - "Vessel": Lex returns to the mansion, after being abducted, with his new powers. When he shows Lana by shooting his hand, they start talking by the stained glass window. The reflections in their eyes are supposed to be the light coming through the window, but are actually from a white screen used for lighting. The reflections in their eyes are rectangular to confirm this.
Continuity mistake: In Episode 22- Season 5 - "Vessel": At the start, Lex wakes up and heads towards an open field many miles away from the mansion. They show a camera shot of his face in the field and the sky is grey and cloudy, but in the very next shot the sky has turned blue and the sun is shining.
Factual error: In the 5th season episode "Lexmas," Chloe says she needs Clark to deliver the Daily Planet's Toys For Tots contribution because of a Teamsters' Strike. However, the Toys For Tots program is run by the United States Marine Corps Reserve, and collection and distribution is handled by Marines and Reserves. The Teamsters have nothing to do with it.
Revealing mistake: At the beginning of No Mercy - Season 5 Episode 19, Lional's limo comes to a screeching halt on railroad tracks. The camera is panned out to where you can see this happen. The black tire marks that are supposed to appear from the hard braking are already present, which means there were multiple takes.
Character mistake: While Clark and Chloe are at Daily Planet, Clark asks her what is wrong with her mother. Chloe responds that her mother left when she was twelve years old. In the episode Lineage, Chloe and Clark are looking for Rachael Dunleavy and Chloe says her mother left when she was five.
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: Chloe is sneaking around inside the warehouse that Lex is using to hide the space ship. After she is found by a security guard she turns back around to look in where the ship is. When she does a shot from her POV shows the fan blades spinning faster then they were in the shot before and after when we are looking at Chloe through the fan.
Plot hole: Clark uses his X-Ray vision to see the remains of the girl in the wall, which seems to establish the wall is not made with lead. However, he only reacts to the Kryptonite bracelet inside until he is aware it is there, despite the fact he should have been able to feel its effects long before that.
Plot hole: At the start of the episode Samantha is shown putting the sniper rifle together during the start of the speech. The second time we see this scene, after getting the backstory during the rest of the show, the scene plays out that Samantha is backstage kidnapping Lois at the start of the speech. This would mean that Samantha would have to be in two places at once and she doesn't have any powers at all.
Continuity mistake: At the Daily Planet, after the opening credits, Clark tells Chloe that he found his mom unconscious in a field. He did not find her in a field, he found her in the driveway in front of the house. Later, at the hospital, Clark tells his father that he found her in the driveway.
Plot hole: Chloe has to use Lex's thumbprint to access the safe inside level 3. She gets his fingerprints by lifting it off of the flashlight he picked up for her earlier in the caves. The problem is when Lex picked up the flashlight and gave it to Chloe he had only touched the back half of the flashlight, but when Chloe lifts Lex's print she gets it from the opposite end. Since Lex did not touch that end there should be no fingerprints for her to lift and use on the security door.
Continuity mistake: As Chloe is trying to get Clark to help her deliver presents Clark says "Chloe, you didn't have to go there." Right before he says this the two of them start rounding the corner to go down the next hallway. As he is saying the line they are back in the first hallway and start rounding the corner again.