
The One With Ross' New Girlfriend - S2-E1
Visible crew/equipment: When Rachel's at the airport and freaks out after seeing Ross with Julie, right before she steps up on the chair the grey crash mat can be seen on the floor, behind the man who's wearing white pants and is seated.

The One Where Rachel Finds Out - S1-E24
Visible crew/equipment: When Rachel leaves the apartment to catch Ross before his flight, just as she opens the door a crewmember's sleeve and equipment are visible at the left side of the screen.

The One with the Evil Orthodontist - S1-E20
Visible crew/equipment: While Chandler's sitting at the table waiting for the phone to ring, Joey rushes into the apartment because of telescope guy, and when Rachel walks out of her bedroom the reflection of studio lighting rigs can be seen at the top of Monica's TV screen.

The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Rachel and Ross are in the apartment with Marcel, who's still wearing the pink tutu, the bottle of wine can be seen on the side table beside the teapot, but when Ross remembers the wine it's now between the teapot and the couch.

The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Monica takes the newsletter from Rachel it's open to the pages with engagement news, and we can see the left page has pictures as Monica reads Mindy and Barry's notice on the right page, but when Monica wiggles out of her comment about Mindy being pretty that left page is now only words at the bottom, even though she's still open to the same page with Mindy and Barry's notice.

The One with George Stephanopoulos - S1-E4
Visible crew/equipment: At the end, while Rachel's on the phone talking about the Visa card, in the shots facing Monica, Phoebe, Joey, and Chandler when they're playing Twister, the end of the set wall can be seen at the right side of the screen. (00:15:10)

The One With The Girl Who Hits Joey - S5-E15
Other mistake: When Ross and Phoebe are eating cheese puffs and party mix out of the bags, Phoebe's bag reads "Heez-I" instead of Cheez-It, and the brand "Sunshine" has been covered.

The One With Rachel's Assistant - S7-E4
Visible crew/equipment: After Monica tells Chandler the secret about Nancy from Phoebe's old massage place getting fired, when it cuts to the wideshot of the apartment while Rachel's standing by the fridge, we can see the camera at the left side of the screen.

The One In Massapequa - S8-E18
Visible crew/equipment: After the anniversary party, when Rachel and Ross are back at the apartment and Ross tells her that it was the easiest four hundred bucks he ever made, Rachel gets up and just as she walks around the couch we can see the reflection of the cameraman/crew member in the mirror on the wall, at the right side of the screen.

The One With the Baby on the Bus - S2-E6
Visible crew/equipment: While Phoebe's outside Central Perk singing loudly Rachel introduces Stephanie, and just as the audience claps a camera can be seen at the right side of the screen.

The One After Joey And Rachel Kiss - S10-E1
Visible crew/equipment: After Monica whips her hair around and smacks herself in the face with all the shells in her hair, it cuts to Ross at his apartment, and the end of the set wall can be seen at the right side of the screen, with the sound stage visible. (00:21:45)

The One With The Worst Best Man Ever - S4-E22
Visible crew/equipment: In Joey and Chandler's apartment, when Joey is with talking to the stripper about the duck and chicken, the edge of the set is visible where Joey's bedroom is supposed to be. The wall stops short after only a couple feet [widescreen version]. (00:09:00)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: When Ross says he could escape from any uterus, Joey is holding two small books. In the next shot they have vanished and he is holding a large book. (00:02:10)

The One With The Bullies - S2-E21
Continuity mistake: When Phoebe calls by the house with the dog, a woman with a handbag is visible in the background, going into her house. About ten seconds later we see the same woman with the handbag walk towards her house again. (00:15:40)

The One With the Male Nanny - S9-E6
Continuity mistake: Towards the end, during a scene at Ross and Rachel's, Sandy picks up two puppets and puts them on each hand. He starts pulling the blue one onto his left hand, but when the angle changes there's a yellow one on his left hand, and a blue one on his right. It cuts to Ross, then when we go back to Sandy they've changed hands again. (00:24:30)

The One With Joey's Award - S7-E18
Continuity mistake: When taking Jessica's award, Rachel opens the door. But when the camera cuts, Joey is first through the door. (00:18:40)

Revealing mistake: In the one after Monica and Chandler get married, Chandler says he can't dance because his shoes are slippery. If you look closely, he managed to slip so much by standing on the bottom of Monica's dress, not because of the shoes. (00:06:00)

The One With The Rumor - S8-E9
Continuity mistake: The gang confronts Ross over his affair with a fifty-year old librarian when he was younger. If you watch the mirror behind him (in one of the girls' rooms), it changes angles every time the camera cuts between Ross and the rest of the gang. (00:17:40)

The One with George Stephanopoulos - S1-E4
Continuity mistake: Just before Ross gets hit in the hockey game, you can see him wearing a foam finger which then disappears. (00:11:45)

The One With All The Thanksgivings - S5-E8
Continuity mistake: When Phoebe's trying to make the TV work at the beginning, in the close-ups and the first wide shot the remote's at an angle, but in the second wide shot it's straight. It then goes back to being at an angle. (00:00:15)
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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