The One with Two Parts: Part 1 - S1-E16
Continuity mistake: When Ross, Carol and Susan are watching the birth video, Ross has his hand on the fake baby's head. In the next shot his hand is on its shoulder. (00:15:50)
The One with Two Parts: Part 1 - S1-E16
Continuity mistake: When Ross says he's going to be a father, Chandler drinks from his cup. In the next shot the cup is gone. (00:16:55)
The One with Two Parts: Part 1 - S1-E16
Continuity mistake: Towards the end, as Joey is leaving Central Perk, Rachel's posture goes from leaving over the back of the sofa with her hands clasped to standing up with her hands on the back of the sofa. (00:18:15)
The One with Two Parts: Part 2 - S1-E17
Continuity mistake: When Joey is talking to Ross and Chandler about missing Phoebe's birthday, Chandler has the newspaper in his hands. In the next shot, you can see that Chandler does not move at all, then in the next shot, the paper is on the table. (00:04:35)
The One with Two Parts: Part 2 - S1-E17
Continuity mistake: Just before Ross drops the cake, Rachel is pouring crisps into a bowl with her left hand holding the bottom of the bag. In the next shot, she is holding the bottom of the bag with her right hand. (00:05:50)
The One with Two Parts: Part 2 - S1-E17
Continuity mistake: After Ross drops the cake, when everyone gathers around the table, there is a shot of Monica with no one behind her. In the next shot, Phoebe has appeared next to the lamp behind Monica from nowhere. (00:06:30)
The One with Two Parts: Part 2 - S1-E17
Continuity mistake: When Ross and Jack are talking about becoming a father, Ross takes a drink out of a glass and puts it back down. The liquid doesn't move when put back down. (00:08:15)
The One with Two Parts: Part 2 - S1-E17
Continuity mistake: At the end of the scene where Phoebe goes to speak to Ursula, Ursula has some food on her fork. In the next shot it is gone. (00:16:10)
The One with All the Poker - S1-E18
Continuity mistake: When the group is sitting around the table in Monica's apartment playing poker, Monica is making something to eat. When she puts it on the table and sits back, we can see a pile of plates on the table on her right side. But in the next shot, the plates are gone. (00:05:35)
The One with All the Poker - S1-E18
Continuity mistake: When Rachel finds out she has an interview she is holding the letter in her left hand. When the shot changes, the letter is in her right hand. (00:09:05)
The One with All the Poker - S1-E18
Continuity mistake: After the game at Ross' apartment Chandler takes Phoebe's cursed money, and when Ross wants to settle up with "the big Green poker machine who owes fifteen," Rachel's sitting down at the table in front of Ross, but then it cuts to Rachel who's suddenly standing up near the table. (00:12:30)
The One with All the Poker - S1-E18
Continuity mistake: In the scene where Rachel and Ross are playing poker head to head, Rachel borrows $7 from Monica's purse and then puts the purse down on the table. She puts it down on her left hand side but it then switches to her right hand side without her touching it and then back again. (00:22:25)
The One with All the Poker - S1-E18
Continuity mistake: When Chandler and Ross are explaining how Joey cried during their poker game, Joey's coffee mug is blue when he's holding it at the counter, but when Joey walks away from the counter his mug is yellow.
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: At the beginning when Rachel and Monica talk about the free coffee sample, Rachel puts it down on the counter to her right. In the next shot it's lying to her left with no time to have gotten there. After that it switches from the right to the left and back again. (00:01:25)
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Monica looks at Barry and Mindy's engagement notice in the magazine, she folds the page over. In the next shot, the magazine is open in her hands. (00:01:50)
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: After Ross asks Marcel to bring him the rice, he picks up his chopsticks. In the next shot, he is holding a napkin. (00:02:15)
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Rachel asks Marcel 'did you poo in the shoe?' Marcel is leaning on Rachel's arm. In the next shot he has vanished. (00:06:10)
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Ross and Rachel argue about losing Marcel, the bottle of wine Ross re-corks is sitting on the table. Neither of them touch the bottle at any point after this yet when the woman from animal control arrives, the bottle has moved to the side table. (00:10:15 - 00:11:10)
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Rachel tells Ross that she lost Marcel, the bottle of wine has the cork sticking half way out. In the next scene which continues directly on from before as Ross and Rachel argue, the cork is back in the bottle. (00:10:15)
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Rachel tells Ross that she "kind of lost" Marcel it cuts to an exterior shot from the balcony, and if we look past Rachel and Ross we see there's a table against the wall, under the Maïna La Voyante poster, but that table does not exist in previous or following shots. (00:10:15)
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.