The One With Phoebe's Uterus - S4-E11
Continuity mistake: When Phoebe is on the couch in the coffee house, talking to Monica and Rachel, the puppy moves and the way Phoebe is holding the puppy changes between shots. (00:17:00)
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 With The Free Porn - S4-E17
Continuity mistake: Near the end, when Emily walks into the house, the TV should be on with the porn. But instead, it's turned off.
The One With The Fake Party - S4-E16
Continuity mistake: After Rachel spins the bottle and it points to Joshua, when she crawls over to him on her hands and knees the bottle's in front of her knees, but in the next shot facing Joshua the bottle is to her side, near her feet.
The One With The Fake Party - S4-E16
Continuity mistake: When Joey takes the steaks out of the freezer, Phoebe's holding a napkin up by her face with her left hand while her right hand is down and empty, but in the next shot it's her right hand that's up with a napkin.
The One With The Fake Party - S4-E16
Continuity mistake: When Emily says that she'll go first at spinning the bottle we see the door behind Ross is wide open, but after Emily spins the bottle that door is closed, yet it's wide open again during the game and then closed.
The One With Joey's Dirty Day - S4-E14
Continuity mistake: After Chandler gets back from the strip club, when he throws his jacket and scarf they both land on the rug between the recliner and coffee table, but when Chandler sits in his recliner the jacket is gone and the scarf is lying on the floor on the opposite side of the table.
The One With All The Rugby - S4-E15
Continuity mistake: When Rachel comes home and excitedly tells Monica that she felt Joshua's pulse, there are two handbags hanging from Rachel's shoulder which vanish between shots, but then they reappear on her shoulder.
The One Where They're Going To PARTY! - S4-E9
Continuity mistake: When Joanna stops Rachel from leaving work Rachel's holding her handbag and jacket, and there's still one bag hanging on the wall hook, but when Joanna mentions the "drinking binge" there are two bags hanging from the hook, then it's back to just one bag, yet when Joanna calls Sophie there's nothing on the hook and Rachel has both bags.
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 Ballroom Dancing - S4-E4
Continuity mistake: While Treeger chews out Rachel for not properly disposing the pizza box in the trash chute, the room's door is closed, then wide open, and then closed again.
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: Joey is in their hotel room asking Chandler where Monica is, and the open bathroom door behind Chandler alternates from wide open to halfway open between shots.
The One With The Free Porn - S4-E17
Continuity mistake: When Joey is asking Ross why he told Emily that he loves her, Joey's bottle of juice is right in front of him. In the next shot of Joey, there's two bottles - Monica's Diet Snapple and Joey's juice, and in the next shot it's back to one again. Monica's drink appears and disappears throughout the scene. (00:11:25)
The One With The 'Cuffs - S4-E3
Continuity mistake: Joey's encounter with the encyclopedia salesman is riddled with errors. First, when the salesman is talking about Van Gogh and saying "He painted that," he points to a page that is all text; later, Joey is reading about vomit, and it is at a pont much further on in the book than when the salesman read about vulcanized rubber (which it shouldn't be, given the encyclopedia is alphabetized); finally, when Joey buys the "V" volume, as he opens it he has a $50 bill in his hand, and when the shot changes to show the salesman he is somehow folding and pocketing it without having taken it from Joey. (00:13:00)
The One Where They're Going To PARTY! - S4-E9
Continuity mistake: When Chandler answers the phone and it's Gandalf calling to cancel, Ross is just opening the fridge, but the shot cuts to Chandler with the phone and Ross is putting two beers down on the side next to him - too quick to have got them there from the fridge. (00:05:35)
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)
The One With Phoebe's Uterus - S4-E11
Continuity mistake: When Monica is drawing the seven erotic zones, she says there are seven and Rachel says, "Let me see that!" Rachel has one leg on the couch and then in a flash she has them both on the table. (00:14:05)
The One With All The Rugby - S4-E15
Continuity mistake: When Rachel is talking to Joey about flushing the toilet, her hands go from counter to bottle top to counter with no time between camera cuts. (00:02:00)
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: In the episode where Rachel goes to tell Ross she loves him (in England) she leaves her room with a brown sleeveless vest and a cardigan over her shoulders. The cardigan then disappears in all other shots until after Phoebe says "he's in love with the British chippy". Her leather jacket also goes from being in her hands to over her arm. (00:19:30)
The One With The 'Cuffs - S4-E3
Continuity mistake: In Joanna's office, Chandler and Rachel are pulling his pants from one another while he is cuffed to the filing cabinet. Right before Rachel says "What if I clean your bathroom for a month?" she throws the pants onto a chair, but then when Chandler later says "Freedom. I want my freedom. Why won't you hear me?" he opens the door to yell to Sophie and they are both holding the pants again. (00:15:10)
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.