The One With Joey's New Girlfriend - S4-E5
Continuity mistake: Chandler is chasing Kathy down the street trying to get her attention. During a close-up of him running, just before the camera cuts away we see a guy's face on the left; when it cuts back to Chandler he runs for a while and then encounters the same guy (the dog-walker). Also, when he finally lands in front of Kathy, there is a bike rider coming towards them, but as the camera cuts back and forth between the two, the rider never passes them. (00:11:30)
The One With Joey's New Girlfriend - S4-E5
Continuity mistake: When Chandler is chasing Cathy, the mustard on his shirt changes place, size and darkness throughout the scene. (00:11:45)
The One With Joey's New Girlfriend - S4-E5
Continuity mistake: During the scene where Chandler is playing hide and seek with the duck and the chick, the duck moves from facing the opposite way to him, facing the same way, and then the opposite way as Joey walks in. (00:13:35)
The One With Joey's New Girlfriend - S4-E5
Continuity mistake: In the bar, Kathy is trying to set Chandler up with one of her friends. When the camera is facing Chandler, we see Kathy's hand rubbing Joey's back, but when it cuts to a front shot of Joey and Kathy, her arm is down in front of her. Then without having had enough time to move, her elbow is up on the table and she is holding hands with Joey. (00:16:10)
The One With Joey's New Girlfriend - S4-E5
Continuity mistake: When Ross goes to Amanda's house for a date you see her two children sitting on the couch. The little boy with blonde hair is sitting down, when it cuts to Ross and Amanda talking the boy is standing up on the couch, the next shot he's sat down as Amanda walks out the door.
The One With The Dirty Girl - S4-E6
Continuity mistake: At the beginning of the episode where they are watching Ross through the window, Phoebe is leaning forward and standing to the left of the pole next to Chandler. When the shot changes to Ross coming through the door, she is suddenly standing up straight and is now behind Joey and Chandler. (00:00:10)
The One With The Dirty Girl - S4-E6
Visible crew/equipment: When Rachel says, "And not a coupon for an hour of Joey love," the stage lights are reflected in the tv. (00:04:50)
The One With The Dirty Girl - S4-E6
Visible crew/equipment: When Monica leaves the kitchen into the next scene, the boom mic is visible at the top of the screen above the kitchen door for a short period of time. (00:07:40)
The One With The Dirty Girl - S4-E6
Other mistake: When Rachel tells Joey he can't get Kathy another "coupon for an hour of Joey love", you can see Chandler (Matthew Perry) mouthing the words "Joey love". (00:17:21)
The One With The Dirty Girl - S4-E6
Visible crew/equipment: When Monica's explaining why she turned down the catering job, the large studio lighting is reflected on the TV when she tells Phoebe how much money she needs. Then just as Joey and Kathy walk in, the camera can be seen at the left side of the screen.
The One With The Dirty Girl - S4-E6
Continuity mistake: When Ross is making out with Cheryl in her apartment, he gets chocolate syrup on his fingers. In the following shots the chocolate syrup has disappeared. While he wipes his hand on the sofa, no way that would leave his hand perfectly clean.
The One With The Dirty Girl - S4-E6
Continuity mistake: When Ross and Cheryl are standing in the hall outside Cheryl's apartment, she's holding her keys in her right hand when she asks Ross if he'd like to come in, but after Ross makes the joke about Homo erectus, Cheryl opens her hand and the keys have vanished from her hand.
The One With The Dirty Girl - S4-E6
Continuity mistake: Rachel is working on the crossword puzzle and her legs are crossed (first left over right) and they switch back and forth between shots (about four times) without any time to do so.
The One Where Chandler Crosses The Line - S4-E7
Continuity mistake: When Ross is telling Monica and Phoebe that he found his "sound" in college, Monica spits out her orange juice and places the glass on the coffee table. The shot changes to Phoebe and you can see Monica putting the glass down again. (00:03:30)
The One Where Chandler Crosses The Line - S4-E7
Continuity mistake: When Phoebe tells Ross that she wants to hear his "sound", she has her guitar in her lap. The shot changes, she says "Play that funky music white boy," and her guitar is missing. In the next shot, Ross runs out and her guitar is back on her lap again. (00:03:50)
The One Where Chandler Crosses The Line - S4-E7
Continuity mistake: When Cathy and Chandler are talking while sitting inside the boat, the silver object on the corner of the counter behind Chandler disappears between shots. (00:08:20)
The One Where Chandler Crosses The Line - S4-E7
Continuity mistake: When Chandler is showing Joey all of the new stuff in the apartment, the cuff on his right sleeve keeps going from messy to neat between shots. (00:13:45)
The One Where Chandler Crosses The Line - S4-E7
Continuity mistake: When Ross and Phoebe are talking in Central Perk, Phoebe's position changes. (00:14:45)
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
Continuity mistake: In the scene were Phoebe is calling for Monica's eye doctor, in the background you can see the TV is off. Then Phoebe asks if she wants to see the on call doctor, Monica says yes, and in the background the TV is on. (00:03:55)
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.