
Revealing mistake: When Chloe, Eli, Greer, and the rest of the team first go to the alien planet, you can see a car driving in the background to the left of the screen at the beginning of the shot (which wouldn't make sense considering they're on an alien planet). (00:15:40)

Kugelblitz - S3-E4
Revealing mistake: At the beginning of the episode, as Sissy is signing the papers under the pseudonym Dana Pocket, she is holding cash in her left hand. The words "pictures" "and "film" can be appreciated on the faces of the bills, revealing this is fake money, often used in Hollywood productions.

Lead Horse Back to Stable - S1-E11
Revealing mistake: When Danny and Colleen are fighting in the rain at the end of the episode and Danny starts explaining how they should stop fighting, raindrops from the camera can be seen dripping from the top left of the screen.

Chapter 7: The Reckoning - S1-E7
Revealing mistake: There's some sleight of hand involved when Cara gets her cup of tea from the repurposed IG-11. Maybe it was costly to have the animatronic arm working to the point of actually supporting the cup and hand it to her, so pay attention to what Cara actually does; Gina Carano is ALREADY holding the cup, taps the mechanical hand with it as if the fingers just released it from their grasp, and retrieves it. (00:11:50)

Revealing mistake: When Jen is at the cash bar and keeps putting money down, it's the same shot used multiple times since it's the same serial number on the $5. And in one shot they flipped the image to make it look different (you can see the "5" is a reverse image).

Revealing mistake: When the target's iPhone rings and Christopher Chance answers it, he swipes his finger across the bottom of the screen, which is the regular gesture to answer a call on the iPhone. Trouble is that we see the screen at the time, and it's not showing an incoming call, just some sort of list - he swipes his finger over nothing of any significance at all.

Revealing mistake: Right after TJ and friends are looking at the "thermometers" of cans, the Ashleys have at least 4 crates of cans that they bring in on forklifts. However, the end result is 4,362 cans for the Ashleys. This may seem kind of picky, but I think there was more cans than 4,362.
Suggested correction: This is literally just an assumption, and nothing else. 4,362 is a pretty huge number, and with the amount of cans that we see the Ashleys collect in the episode, combined with the amount of cans that they and the rest of Miss Furley's class collected off-screen, it is perfectly believable that Miss Furley's class would end up collecting that amount of cans.

Super Nova - S1-E2
Revealing mistake: When Stan, Xev and Kai are walking to the Memory Chamber, they seem to walk out of a two dimensional line at the lower left into the scene. The set and green screen weren't quite synched.

Rejoice! I Am Ultimo Thy Deliverer - S1-E2
Revealing mistake: When Mandarin and Modok are flying towards Ultimo in order to regain control over it, there is a noticeable jump cut, as evidenced by the clouds in the sky suddenly changing.

Farewell My Beloved Witch - S1-E3
Revealing mistake: When Lupin is saved by Fujiko and is on the ladder, his lower left leg is missing. (00:21:05)

When in Rome - S1-E3
Revealing mistake: Will and Frankie are in a boat. In the first wide shot the boat is going rather slowly, in the next shot they are speeding many times faster, and the shot is erratic, showing that the action was speeded up. (00:02:05)

Revealing mistake: There is more mud makeup on the stuntman playing Virdon than there is on actor Ron Harper (Virdon) himself.

Dawn and the Haunted House - S1-E2
Revealing mistake: Stacey can be heard whispering instructions to the kids she and Dawn are watching.

Revealing mistake: When everyone is supposed to be frozen, the neighbor girl standing behind the car can be seen moving her hand onto the car. This happens as Monica says "I'm not afraid of you, Wanda." (00:24:25)

Revealing mistake: After Max the dog breaks free from the cage and then bites through Callahan's chains, the two head to the metal barred window and Max begins pulling on one of the bars with his teeth. Which are obviously rubber, as they 'bend' slightly as the dog is pulling.

Revealing mistake: When Major Popov aims the rocket launcher at the Venus probe, there is no rocket in the launcher- it is just an empty tube.

Not Kansas - S3-E21
Revealing mistake: As the guy fires the machine gun at Guardian, there's a closeup of bullet casings falling to the ground, but they're not just empty casings, they're fired blank rounds.

Revealing mistake: In the closeup of Twiki, you can see Felix Silva's mouth in the mouth grille.

The Resurrection of Joe November - S3-E24
Revealing mistake: Stock footage used for the Mardi Gras scenes shows a crowd dressed in 20th Century clothing.

Flash Gordon and the Planet of Death - S1-E1
Revealing mistake: In the flashback of the scientists' fate on the planet of Death, the sole survivor manages to run away and avoid the ray of "Belfagore" (which is just a big flashlight). Problem is, he does not; before hitting Bending behind him, the beam fully lit up his back, but he suffers no adverse consequences, no dropping dead for Jefvus. (00:06:40)