
The One with Mrs. Bing - S1-E11
Continuity mistake: When Joey shows Ross the photo of his parents wedding, Ross is holding a magazine. In the next shot, the magazine is gone. (00:15:00)

The One with Mrs. Bing - S1-E11
Continuity mistake: The way Joey holds the picture of his mum changes between shots. Note his fingers. (00:15:50)

The One with Mrs. Bing - S1-E11
Continuity mistake: When Coma Guy asks who Monica and Phoebe who they are, he has his hands lowered on the bed in one shot and raised outstretched in the next. (00:18:30)

The One with Mrs. Bing - S1-E11
Continuity mistake: In the final scene Rachel passes out copies of her draft for her book. She gives out all her copies and asks for their opinion. However, near the end of the scene after waving her arms around empty handed a copy of her script magically appears in her hands. (00:21:10 - 00:21:45)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: During the song at the beginning of the episode, keep your eye on Ross's mug. He is holding it in his lap, then there is a shot of Monica with Ross's empty saucer on the table. In the next shot, the mug has appeared on the saucer. (00:00:30)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: When Ross says he could escape from any uterus, Joey is holding two small books. In the next shot they have vanished and he is holding a large book. (00:02:10)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: When Ross is on about calling immigration, his hands move with no time to do so. (00:04:05)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: When Ross visits Carol, he hugs her, and puts his hands on her hips. In the next shot, he isn't touching her and has taken a step back instantly. (00:05:10)
The One with the Dozen Lasagnas - S1-E12
Continuity mistake: When Paulo is about to get his massage, he puts his hand on his hip. In the next shot, he is leaning forwards and both hands are out strecthed in front of him. (00:09:00)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: When Rachel is talking with Phoebe about Paolo,. she unrolls some kitchen paper and uses it as a tissue. Initially she's holding two torn halves attached to the roll, then when saying "He's a pig" it goes to a whole sheet not attached to any others, then when she sits down it's a whole sheet attached to the roll again. Plus when Phoebe sits too, in some shots the paper is on the table, in others it's not. (00:15:20)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: During the scene where Phoebe is telling Rachel that Paolo made a pass at her, Rachel unrolls a long length of kitchen roll. During the scene there is a shot over her shoulder where we see that the kitchen roll is as normal and in the next shot we see it unrolled again. (00:15:30)
The One with the Dozen Lasagnas - S1-E12
Continuity mistake: Second time we see Monica score on the foosball table, she spins the rod closest to the goal. The camera changes and the ball is hit from the rod furthest away from the goal. (00:17:35)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: In The One Where Ross Finds Out he's having a boy (series 1), just before Rachel lets it slip, she is sitting on the edge of a chair eating a cookie. Watch her dress, it changes back and forth from being undone from the waist up, to only having two buttons open at the top. (00:19:55)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: At the end of the episode, when Monica scores a goal against Joey and Chandler, she is playing with the red team and scores with her strikers. In the next shot, a blue midfielder scores the goal. (00:21:05)

The One with the Dozen Lasagnas - S1-E12
Continuity mistake: In the scene where Phoebe confesses to the gang that Paolo made a pass at her, it is pitch black outside. When Joey and Chandler turn around after heading for the door, it is sunny outside.

The One with the Boobies - S1-E13
Continuity mistake: When Phoebe's boyfriend is talking about Chandler at the coffee shop, the cookie he is holding jumps from his left to his right hand in an instant between shots. (00:03:20)

The One with the Boobies - S1-E13
Continuity mistake: The way Rachel is sitting when discussing seeing Chandler naked is constantly changing. (00:07:00)

The One with the Boobies - S1-E13
Continuity mistake: When Joey's dad walks in and sees Ronnie, he shuts the door. However, as they go to leave to a hotel the door is open and Joey shuts it. (00:11:50)

The One with the Boobies - S1-E13
Continuity mistake: When Joey's mom comes to tell him that she knows about the affair, he places the paper bag that she brings on the stove and it falls over. In later shots, it is obvious that the bag is upright. (00:17:05)

The One with the Boobies - S1-E13
Continuity mistake: When Joey finds out that his mother knows about his dad's affair, she tells him she's fine and holds her hands to her chest. In the next shot her hands are outstretched in front of her. (00:17:10)
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.