The One With The Joke - S6-E12
Continuity mistake: In the coffee house scene when Joey reveals that he is working there, the strap on Joey's apron goes back and forth from being twisted around his neck and then straightened out. (00:10:50 - 00:12:50)
The One with the Candy Hearts - S1-E14
Revealing mistake: When Chandler bangs his head on the bathroom wall after realising Janice is at the restaurant, the wall wobbles, revealing it is part of the set. (00:04:15)
The One Where Nana Dies Twice - S1-E8
Visible crew/equipment: When Monica and Ross meet up with their parents and their nana, a boom mic is visible at the top of the screen. (00:04:20)
The One Where Underdog Gets Away - S1-E9
Visible crew/equipment: When Chandler runs into the apartment to say Underdog has gotten away, a crew member can be seen reflected in the sun shaped mirror behind him walking through the back of the shot. It can't have been Rachel, Monica, Phoebe or Joey because Joey is sitting down and Rachel, Monica and Phoebe are nowhere near the mirror. (00:14:05)
The One With Barry & Mindy's Wedding - S2-E24
Revealing mistake: When Chandler finds out that his online girlfriend is married, the camera cuts to Joey, and you can see the computer screen is off.
The One Where Rachel Finds Out - S1-E24
Other mistake: When Rachel leaves the apartment to pursue Ross to the airport, she is turning to the left when she exits the apartment. The stairs are to the right.
The One With Ross's Library Book - S7-E7
Continuity mistake: When Monica says, "she's not going to like that chicken either," Chandler's arms are crossed. Then the shot changes, and they're now by his face. (00:07:50)
The One Where Rachel Finds Out - S1-E24
Continuity mistake: When Rachel and Monica are discussing whether or not Rachel should meet Ross at the airport she's taking a bottle of red wine out of the refrigerator, but when she places it on the table in the next camera shot the bottle of wine is suddenly a bottle of white wine. (00:16:25)
The One With The Embryos - S4-E12
Visible crew/equipment: In the shot where Monica suggests that Ross creates the questions, there is a red boom mic followed by a blue boom mic at the top center of the screen. (00:05:15)
The One Where Rachel's Sister Babysits - S10-E5
Continuity mistake: While everyone is booing Mike and Phoebe, the guy sitting behind Phoebe changes position in every shot.
The One With The Soap Opera Party - S9-E20
Visible crew/equipment: After Ross introduces Charlie to Phoebe and Monica in Monica's' apartment Charlies' cell phone rings. She turns around and in the back where the "secret closet" is, you can see on the left corner two spotlights.
The One with the Stoned Guy - S1-E15
Other mistake: Mid episode when Monica turns off the cordless phone after being told by Wendy that she can not make it, the phone makes the "out of range" audio tone instead of the "power off" audio tone. Occurs directly as Monica says, "Wendy, we had a deal, yeah, you promised. Wendy, Wendy, Wendy.".
The One With Christmas in Tulsa - S9-E10
Continuity mistake: When Wendy is coming onto Chandler her hands are at the top of his tie. When the shot changes, her hands are halfway down his tie.
The One With Ross's Wedding, part 2 - S4-E24
Other mistake: When Emily first walks in wearing her wedding dress, there is a distinctive difference between that dress and the one Monica picked up from the store a few episodes earlier and tried on (yes, more than that she is also wearing a jacket). There is a band of material at the top of the dress when Emily is wearing it that was not there when Monica wore it.
The One Where Chandler Crosses The Line - S4-E7
Continuity mistake: In the final scene wherein Phoebe finally agrees to play guitar again, Ross moves from the armchair to the sofa. As he sits down, his arm is by his side, but when the camera angle shifts, it is on the back of the sofa. (00:20:50)
The One With Chandler In A Box - S4-E8
Visible crew/equipment: Just as Ross asks Rachel for the necklace he got her, a stage light is very visible above the bathroom door. (00:12:35)
The One With The Worst Best Man Ever - S4-E22
Continuity mistake: In the scene where the veterinarian gives the ring back to Ross, there is a dog in the background that goes from standing up to lying down to standing again depending on the shot.
The One With All The Kissing - S5-E2
Visible crew/equipment: When Rachel tells her date she's going to have to take a rain check and goes back into the apartment, as she opens the door you can see a cameraman standing inside the apartment. (This is only visible in the broadcast version, not DVD or widescreen). (00:10:45)
The One With The Chicken Pox - S2-E23
Factual error: Ryan is a LCDR submariner, who had been on a sub deployment for the last two years. but at no time does he wear his dolphins pin. A true submariner would sooner forget his skivvies than his pin.
The One With The Apothecary Table - S6-E11
Continuity mistake: When Phoebe and Rachel are first talking about the apothecary table, there are two piles of CDs on it. In the side shot you can see that the two CDs on the top of the pile in front of Rachel are overhanging by a few centimetres. A few shots later, however, the top two CDs are overhanging on a different side. (00:06:05)
Answer: Usually by the seventh night of Hanukkah you don't know what to get the other person, and you will probably resort to getting the other person something insignificant. Chandler is basically saying that the pen is a stupid gift.