The One Where Joey Speaks French - S10-E13
Visible crew/equipment: After Rachel tells the others that her father had a heart attack and Ross takes two of Monica's cookies, when it cuts to the shot of Central Perk it's from a low angle, and the studio lighting rigs at the ceiling can be seen through the windows.
The One With Joey's Fridge - S6-E19
Visible crew/equipment: When Professor "Frei.sen.stin.linder" walks in on Ross with Elizabeth, it then cuts to Ross, Chandler, and Joey walking into Joey's apartment, and we can see the opening in the wall where the bulletin board usually hangs.
The One In Vegas, Part 2 - S5-E24
Visible crew/equipment: At the start of the Netflix version, when the recap scenes from 5x23 Part 1 are being shown, in the shot of Phoebe, Monica, and Chandler on the airplane the end of the cabin set can be seen beside Chandler, at the right side of the screen.
The One In Vegas, Part 1 - S5-E23
Visible crew/equipment: While Phoebe, Monica, and Chandler are with gladiator Joey in the casino, Joey notices the tension between Chandler and Monica, and when he asks what's going on a tape mark can be seen on the floor at the feet of the extra standing at the slot machine, then more tape marks can be seen at the same spot after Monica sarcastically wishes Chandler happy anniversary.
The One With The Mugging - S9-E15
Visible crew/equipment: When Chandler first walks into the conference room at work, and also later when he walks out of the conference room while using a cane, the end of the set wall can be seen at the left side of the screen.
The One Where Old Yeller Dies - S2-E20
Visible crew/equipment: Chandler and Joey are spending time with Richard; as they play foosball and Richard scores, he leans back and says "Could that shot BE any prettier?" in a mockery of Chandler. The end of the wall and the hallway behind it are visible (ie the wall set ends). (00:16:00)
The One With The Red Sweater - S8-E2
Continuity mistake: Monica is sitting in the living room with all her wedding presents, waiting for Chandler to return. She begins to open a large parcel and reveals a brown cardboard box. Then the camera moves to Joey, and when it moves back, the parcel is wrapped up again. This happens about three times. (00:05:05)
The One With The Apothecary Table - S6-E11
Visible crew/equipment: After Janine tells Joey that she'll apologize to Monica, in the shot of Janine walking into the hallway the end of the hall's set wall can be seen at the left side of the screen, and the corner of the camera can be seen moving at the right side of the screen.
The One With All The Wedding Dresses - S4-E20
Continuity mistake: Ross comes into Chandler and Joey's apartment to ask the guys and Rachel what they are doing in four weeks, the Magna Doodle behind him first says "poop", then is blank. We cut to Joey checking his diary, cut back to Ross, and it now has "get out" written on it. [Fullscreen version]. (00:10:35)
Revealing mistake: In the episode where Joey is doubling Al Pacino's butt you can clearly see his shadow when he's shooting the scene in the shower, and he's wearing boxer shorts. (00:13:20)
Continuity mistake: The number of the flats near the start of the first series was 4 and 5. After a few shows they changed to 19 and 20. [The producers realised that the numbers 4 and 5 were for apartments on the lower floors and had shown Monica's apartment to be much higher up so they changed the numbers - it's still a mistake but there's the reason.]
The One With Phoebe's Ex-Partner - S3-E14
Visible crew/equipment: When Phoebe and Leslie finish singing the song Sticky Shoes, as they're hugging each other in the side shot, the second camera can be seen at the left side of the screen. (00:13:00)
The One With Phoebe's Ex-Partner - S3-E14
Visible crew/equipment: After Ross finds out that Mark quit his job, when Rachel and Ross leave the office, the second camera can be seen as the shot pans to the right, at the right side of the screen. (00:06:15)
The One With The Worst Best Man Ever - S4-E22
Visible crew/equipment: While Joey, Ross, and Chandler are waiting at the vet's office, in the following flashback scenes with the duck, when Joey bathes the duck the end of the bathroom set wall can be seen at the right; and when Chandler's sitting in the canoe with the duck in the pail, a crewmember can be seen where the set wall ends. (00:19:45)
The One with George Stephanopoulos - S1-E4
Visible crew/equipment: When the guy delivers the wrong pizza, in the shot after Monica grabs the pizza box to hand to Phoebe and shouts that they have George's pizza, the tape marks can be seen on the floor with one of them between the delivery guy's feet.
The One With Chandler In A Box - S4-E8
Visible crew/equipment: After Kathy tells Chandler goodbye and leaves Joey lifts the lid from the box, and when Chandler stands up in the box we can see the end of the living room set wall and the pink set wall.
The One With The Princess Leia Fantasy - S3-E1
Visible crew/equipment: After Phoebe's Princess Leia impersonation in front of Ross it cuts to Joey watching Wheel of Fortune, and in the next shot as Chandler walks in the camera can be seen at the right side of the screen.
The One With Rachel's Date - S8-E5
Visible crew/equipment: While Phoebe and Tim are at Central Perk, when Tim's beeper goes off he blows Phoebe a kiss when he leaves, and as Phoebe catches that kiss and throws it away have a look at the left side of the screen, where the Central Perk wall ends we can see part of Monica's restaurant kitchen set - the door and the wall beside it. (Widescreen version).
The One Where Rachel Tells... - S8-E3
Continuity mistake: While Joey's on the phone with Monica telling her the phony story that he and Phoebe smell gas coming from her apartment, on the table are the glass casserole dish and lid from the chicken parmigiana and a water bottle, but in the closeup there's only a ceramic blue bowl filled with eggplants and squash, and it keeps switching in the following shots,.
The One With Phoebe's Husband - S2-E4
Visible crew/equipment: After the opening credits, just as Joey says that it's unbelievable Phoebe can be married, a camera and yellow electrical cord can be seen at the left side of the screen, and a bit of it is still visible in following shots when Monica mentions the cheeseburger.
Answer: These are references to the TV show NYPD Blue. Deputy Andy Sipowicz is the name of one of the characters, whilst another character (Deputy Danny Sorenso) is played by Rick Schroder who previously starred in the show Silver Spoons.
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