
Revealing mistake: While Andy, Aunt Bee, and Opie are at the Hollywood studio watching a scene being filmed, when Andy mistakenly stands up and interrupts the filming we can see the wall and shelves behind the director, and it should look familiar because it's the wall and shelves from Floyd's shop in Mayberry.
Super Grover

Revealing mistake: At the end of the episode when Tuco shows up at Walter's house in the backseat of Jesse's car, he tells Walter to get in. As they drive off, the shot pans out to show the street sign across from Walter's house. The sign says Piermont, which is the real name of the street. In the show, the Whites live on Negra Arroyo Lane. (00:48:00)

Revealing mistake: As the gang drives up to the space-ship diner, cars are whizzing by in the background. When they are driving to the base there's also a clip of a fire truck going down the highway in the distance.

Revealing mistake: When Carrie phones Doug at IPS, Doug goes to press the button on the phone for the correct line, but doesn't press any and continues to talk to Carrie. (00:07:40)
Ssiscool

The One With Rachel's Date - S8-E5
Revealing mistake: In the scene in the coffee house, Phoebe is talking to Monica who is drinking a cup of coffee. Towards the end of the scene, the camera is on Phoebe who is smiling & laughing at Monica. In the right hand corner is a side view of 'Monica' however, it is not Courtney Cox in the scene, but a completely different actress. [Widescreen version only, although the "wrong" nose is visible in the original]. (00:06:20)

Revealing mistake: When Laura picks up Baby Rose from Thomas Stark, the blanket is flipped up and you can see a plastic doll's leg, then when she goes into the bedroom, she has the real baby.

The Magician - S3-E4
Revealing mistake: When Oliver meets Thea at the Grind and Jot Cafe (Which looks unsurprisingly like CC Jitters) you can see the cups on the table are from CC Jitters. (00:20:50)

The Treaty - S4-E7
Revealing mistake: Tom is talking on the phone in Ron's office. When he turns the phone at an angle the call home screen that has the end button, the speaker button, etc. turns to its side, which means it was a picture - he wasn't actually calling anyone. (00:02:25)
Tixhe
Revealing mistake: At the apartment complex fire, after Johnny is knocked unconscious by the explosion, when the Pasadena fireman finds him and has to lift him up, it's funny how even though Johnny's unconscious we can see that he actually helps to stand himself up, so the fireman can lift him up and carry him out.
Super Grover

Revealing mistake: It is obvious a dummy was used for the scene of the lighthouse keeper falling to his death.
Scott215
Broken Link - S4-E26
Revealing mistake: During the fight between Garak and Worf near the end of the episode, a Jefferies tube door is knocked out of its frame to reveal the end of the set - a dark room with a wooden scaffold and various other pieces of equipment. (Slow-mo helpful but not required)

Revealing mistake: After Rygel realizes that he can loosen the soil with the dumped gruel, it cuts to John and Aeryn as they approach the Tavlek camp, and when Aeryn tells John, "I am going to take out every last Tavlek. No survivors. No mercy. Now give me the oculars," John holds up the syringe (with Zhaan's sleep mist) that Aeryn had given him earlier, and we can see "DG-4" engraved on the side of the gun, revealing that the prop dept used the model DG-4 aluminum air blow dust gun to play the part of the syringe.
Super Grover

The Night of the Bubbling Death - S3-E1
Revealing mistake: As West drags the body of a bad guy out of the scene, the supposedly unconscious man is holding his head up so as not to have his head dragged through the dirt. A truly unconscious person's head would flop back on to the ground.

Revealing mistake: When Shannon walks into the kitchen and gives Stephanie a hug, in one shot of the highchair where Tommy is sitting there is now a doll.
Bowling255

Subway Wars - S6-E4
Revealing mistake: When Ted uses his laptop to get directions to the restaurant, Bing shows Los Angeles (where it's filmed) as their current location, instead of NY where the show is set. (00:02:15)
renanmister
Revealing mistake: Season 3, Episode 68, "The Duel": The prop wash from the helicopter filming the overhead scenes are evident as everything (dust, twigs, leaves, etc.) is being blown around.

Mr. Monk Meets Dale the Whale - S1-E4
Revealing mistake: When Monk is showing how Dale and his Doctor murdered the judge one can see that the knitting of the right chair is already cut to ensure that the policeman will fall through it when he later steps on it.

Revealing mistake: When Aaron is pinned down by the sewer zombie, the zombie actor's neck can be seen below his head mask.

Revealing mistake: When Sara Tancredi is pulling her dead father off the door he lets out a very audible grunt and you can see his eyes and mouth moving around, a few seconds later he is on the floor and his eyes are dull and his skin slightly pasty. (00:16:40 - 00:17:05)

Revealing mistake: When they are watching for vases, the auction website has no proper domain. It is loaded locally from the C:\ drive. (00:55:00)
Suggested correction: Depending on the location settings on his laptop, they could be giving a false reading. My laptop shows I'm in Cardiff Wales while in fact I'm nowhere near.
SsiscoolThe show was actually filmed on a film set in Los Angeles which is probably why the laptop says Los Angeles as the current location. This most probably slipped past the editing crew.