Revealing mistake: Season 5 Episode 18 "Spark of Life": when they show a closeup of the badly-burned woman during her debridement, it can be seen that even though her eyebrows and hair and, in fact, 90% of her skin has been burned away, she still has long, full eyelashes.
Revealing mistake: While Rory and Lorelai are in the kitchen, in a few closeups of Rory we see the refrigerator and counter area with the microwave, etc. behind Rory, but when Lorelai is at the back door about to join Luke, part of the set beside the refrigerator is gone. (00:04:15)
Revealing mistake: When Wanda traps Magneto in the force field thing, for one shot, Magneto is missing a sleeve on one arm, then it comes back a shot later.
Delenda Est - S3-E11
Revealing mistake: When Dylan and Tyr head to a bridge where supposedly the power source is located as well as Rommie, they start to cross the bridge. As the camera is facing Dylan and Tyr, the next scene two aliens teleport in. Rewind the video to facing Dylan and Tyr and play in slow motion. Watch the bottom portion of the screen and notice the top portion of one of the alien's head go into the camera as if the aliens walked into position for the teleportation.
End Game (1) - S8-E7
Revealing mistake: Boyd has a video-conversation with Linda on the phone she sent him. On top of the screen you can see how long the video will last (1 minute and 3 seconds), showing it's a pre-recorded video, not an actual live conversation.