Visible crew/equipment: After the scene transition from when Clark throws Jonathan into the truck after being exposed to Red Kryptonite, the camera pans around Jonathan with his shirt off; on the left-side of the screen we see a man with sunglasses on who has no earthly right to be there just randomly on the Kent Farm. (00:16:23)
Phoenix (2) - S3-E2
Revealing mistake: When Clark rips the door off the Lincoln, you can see there's no interior panel or door glass.
Plot hole: In this episode, Pete comes across Clark's spaceship in a field, where it landed after the tornadoes hit the town during the last episode of Season 1. The Kents knew the spaceship was gone, and of course it was important that they attempt to get it back as soon as possible so it doesn't fall into the wrong hands. With Clark's speed and X-Ray vision, he should have been able to find the ship after not too long of a search (especially since it was within a few hundreds yards of a road). It seems implausible that he would not have looked for it, given its importance.
Other mistake: Maddie and her father can control only glass, but when at the Talon he uses his powers to pull the diamonds out of the stained glass. Diamonds aren't glass.
Suggested correction: This may not necessarily be true by the way their powers work. Remember, diamonds are a form of rock that are clear. Glass is made from melted sand, which is a ground up type of rock that becomes clear. The similarities between diamonds and glass are enough that it is possible they could still do this.
Diamonds are compressed carbon, not a form of rock. Glass is melted silicon. They're both clear materials, that doesn't mean they're equivalent, otherwise they'd be able to control clear plastic or any number of other things too.
If more explanations of their powers were discussed in the show, one might be able to conclude they do or do not have power over diamonds. However, the script only states they have power over glass, they show no propensity for power over sand itself, or other rocks and minerals. As scripted, this remains as error as it go against what is established.
Factual error: When the bug kid crashes his car, he's driving a VW Beetle, which has the motor in the rear, therefore would not have shut off in a head on collision.
Visible crew/equipment: When Lex and Chloe are talking after the morgue, you can see a crewmember passing behind her at 30:53. (00:30:53)
Suggested correction: You see a person walk behind her in a corridor. Since it is very obvious and occurs during a short cut where nothing else is happening, it is deliberate. A fundamental rule on film sets is that once "action" is called, no-one moves if they don't have to. If a crew member had walked through the shot like that, they would have done a new take or just use a different segment of the shot.
Continuity mistake: When Clark exits the phone booth wearing his blue shirt, only the neck button is unbuttoned in the wide shot. Immediately in the next close-up shot, two buttons are undone. Then in the next shot of Clark's front side, the shirt is back to only the neck button being undone. (00:02:27)
Turbulence - S8-E16
Other mistake: In the article about the plane crash, the last paragraph starts to repeat the same sentence. After is says Mercer took over the operation, it repeats that she started in collaboration with Lex.
Continuity mistake: When Kara and Clark get off the elevator, there's no-one around them as they're walking away. In the next shot of Kara and the elevator, 3 people have suddenly gathered to look at the broken elevator. The elevator was off camera for less than 2 seconds, not enough time for 3 different people to get into the position they're in when they weren't close by to begin with.
Continuity mistake: When Lois is at the dam, looking at the card she previously tore, the numbers and markings are written differently than before.
Continuity mistake: When Lionel is watching the video and drawing Kryptonian symbols, some of the symbols change in between shots. For example, when he draws "minion" one of the dots is touching the square. When he writes the word, everything is nice and neat and the dots aren't touching anything.
Other mistake: When Clark looks at Oliver's newspaper clipping, there's a story about an AIDS hospice being saved. But the 2nd paragraph on talks about the 2nd meteor shower to hit Smallville that has nothing to do with the hospice being saved.
Continuity mistake: After Lois pins the sketch of the Green Arrow, the pushpin changes position. In some shots, it's across the top of the paper and in others it's in between the top of the sketch and top of the paper.
Other mistake: When Clark is in the girl's room and a noise comes from the closet, Clark uses his X-Ray vision to see there's a person in there because he can see the skeleton and is surprised to see it's Lois when he opens the door. However, it's been shown before that Clark can use his X-Ray vision to see objects and people through solid objects. He should have been able to see that it was Lois rather than just a skeleton of an unknown person.
Other mistake: Throughout the series, they reuse the same footage for establishing shots of the Talon. For example, one of the shots has the Talon sign say "Silent Film Festival" with a guy holding and bouncing a basketball as they walk pass the Talon is in s02e05 and s03e11 and other episodes, including s03e10 where it's the same people but the guy is holding his jacket and further back.
Continuity mistake: When Lionel and Lex are talking, after they sit down, near the end of the conversation, Lionel asks who Lex's source is. Lex is looking straight ahead. In the next shot, we see Lex turn his head to face his father. In the next shot, Lex is looking straight ahead again.