The One With All The Resolutions - S5-E11
Continuity mistake: When Joey and Rachel are trying to work out if the other knows about Monica and Chandler, they sit at the table in silence. In a side shot of Joey they look at each other sneakily, and Joey has his arms by his sides. It then cuts to a head-on shot of Joey, and he's got his right arm over the back of the chair. (00:19:00)
The One With All The Resolutions - S5-E11
Visible crew/equipment: Monica and Chandler leave the apartment to go "do laundry," then Phoebe heads out to the airport. When Joey takes a seat, the reflection of camera movement is visible on the window, above the sink. Then Rachel and Joey tell each other they can't share what they each know, and just as Rachel sits down beside Joey, once again we can see the reflection of camera movement above the sink. (00:19:30 - 00:20:20)
The One With All The Resolutions - S5-E11
Visible crew/equipment: After his fiasco with the leather pants, powder, and lotion, when Ross is at Monica's and tells the others he's going to kiss Ben goodnight, as he starts walking to the bedroom the camera can be seen at the right side of the screen.
The One With All The Resolutions - S5-E11
Character mistake: In one of the scenes where Phoebe is teaching Joey guitar, she asks him to demonstrate the "Iceberg" chord. To refresh his memory, Joey refers to the chord as "G Sharp." In reality, the only way to play a G Sharp chord is with a barre chord, and as such the fingering is not exclusive to it.
The One With All The Resolutions - S5-E11
Continuity mistake: Rachel mentions "the big thing," so Joey sticks his fingers in his ears to block her out. When Rachel pulls on his arms, the only things on the table are Joey's bottled drink, crayons, and coloring paper. In the next shot, we see Rachel's arms and she's not holding anything. It cuts to the next shot facing Joey, as he says, "Well then, it wouldn't be a secret, so yeah, that would be OK," and now there's a drinking glass on the table. Rachel removes it in the next shot.
The One With All The Resolutions - S5-E11
Continuity mistake: At the start, when the countdown hits 3-2-1, there's a closeup facing the TV, and in the TV's reflection the couch and armchair are both quite empty, but in previous and following shots both have people seated.
The One With All The Resolutions - S5-E11
Continuity mistake: Immediately when the opening scene starts, we hear from the crowd on the television that there is less than 60 seconds to midnight. However, 60 seconds later in the scene, the countdown still hasn't reached zero.
The One With Chandler's Work Laugh - S5-E12
Visible crew/equipment: After Joey and Phoebe place their betting cash on the counter, when Joey says, "Let's get the contestants out of their isolation booths," the end of the set wall can be seen behind the foosball table. (Widescreen version).
The One With Chandler's Work Laugh - S5-E12
Continuity mistake: During Ross and Janice's conversation in Central Perk, when Ross comments, "You're ending this with me because I'm too whiny?" both his and Janice's left arms are up, but it cuts to the next shot and it's their right arms which are up, then it happens again when Ross says, "I've become so whiny that I annoy you?! Janice!" they both have their right arms up, but next shot it's their left arms up.
The One With Joey's Bag - S5-E13
Continuity mistake: When Chandler speeds up the timer for his turn he places the timer down at the right side of the pillow, but it's at the opposite side of the pillow when he lies down. Then before Monica starts giving Chandler his massage, she sets the timer and places it near the foot of the bed which we see in Chandler's closeup, but in the next shot when she says, "Say goodbye to sore muscles," oblivious to Chandler's pain, the timer is lying by the pillows behind her, near the head of the bed. Note, in the "uncut scene" version, Chandler grabs the timer to speed up his torture, and Monica takes it out of his hand thinking he was going to add more time, then she places the timer behind her. (00:00:25)
The One With Joey's Bag - S5-E13
Continuity mistake: When Phoebe realises she just met her dad she turns to her friends to share the news, and in the closeup she's holding a pair of 3D glasses in her right hand and Monica's holding a pair in her left hand, but in the next wideshot both of those glasses have vanished. (00:09:15)
The One With Joey's Bag - S5-E13
Visible crew/equipment: When Joey walks into Monica's apartment the first time, a stage light can be seen by the window near the bathroom. (00:10:00)
The One With Joey's Bag - S5-E13
Continuity mistake: There is a shot of Phoebe in Central Perk about to talk to Frank (from outside, looking in). From this shot there are several people outside Central Perk. The camera does an instant cut to behind Phoebe, (inside, looking outside) and the people have vanished. (00:15:00)
The One With Joey's Bag - S5-E13
Continuity mistake: When Phoebe is in the coffee house talking to her father and pretending to be the executor of her grandmother's will, after she says "lipstick and a daughter, big day for you" she folds her papers in half, but in the next shot they are unfolded and she then folds them again. (00:15:15)
The One With Joey's Bag - S5-E13
Visible crew/equipment: When Joey walks into Monica and Rachel's apartment to tell the gang he didn't get the part thanks to the bag, as he approaches the couch you can see the end of the stage over Joey's right shoulder. (00:21:15)
The One Where Everybody Finds Out - S5-E14
Visible crew/equipment: When Rachel stands up to get laundry for Monica, a stage light can be seen in the TV. (00:07:20)
The One Where Everybody Finds Out - S5-E14
Factual error: Phoebe holds up a bag of quarters that is almost the size of her head. This would be physically impossible for anyone except perhaps the world's strongest weight-lifters. Quarters are exceptionally heavy for their size. Two rolls weigh exactly a pound. It would take at least 300-400 rolls worth of quarters to fill up the bag Phoebe is holding, which means she is lifting 150-200+ pounds, primarily with one arm. (00:08:40)
The One Where Everybody Finds Out - S5-E14
Continuity mistake: Monica and Chandler are deciding what to do about Phoebe's flirting; the shot cuts to her and Rachel, and Rachel's right hand is on her chin. In the next shot, it's her left hand on her chin. (00:12:00)
The One Where Everybody Finds Out - S5-E14
Continuity mistake: The amount of buttons undone on Pheobe's top by Joey changes after she says, "You didn't rip any buttons." The camera cuts to Joey then back, and it has changed. (00:18:00)
The One Where Everybody Finds Out - S5-E14
Visible crew/equipment: When Ross is using the binoculars to watch Ugly Naked Guy's apartment, the end of the set wall can be seen behind him.
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.