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)
Ssiscool
The One with the Dozen Lasagnas - S1-E12
Other mistake: At the end, Monica is playing as red, but we see the blue team score on the foosball table. However, Monica states that she scored and beat Joey and Chandler again. A previous correction says to look closely as the red team scores, That correction is completely invalid as the player in goal is red. Why would Monica score in her own goal? And Also the blue players can be seen to spin. (00:22:10)
Ssiscool The One with the Dozen Lasagnas - S1-E12
Audio problem: The very last line of the episode (Monica saying "and I'm gone") is an overlay. (00:22:40)
Ssiscool 
The One with the Dozen Lasagnas - S1-E12
Visible crew/equipment: When Rachel's dumping all of Paolo's clothes over the side of the balcony, we can see the apartment's back wall is only half a wall, with the sound stage and equipment at the left side of the screen.
Super Grover The One with the Dozen Lasagnas - S1-E12
Plot hole: At the end, Phoebe and Monica are sitting at the table eating the meat lasagna. Phoebe would not eat this as she is a vegetarian. (00:21:35)
BoobraSuggested correction: Early on in the episode, Monica suggested vegetarians can scrape. It is possible that Phoebe is doing exactly that. Also, two episodes later ("The One with the Candy Hearts"), it is revealed that Phoebe, in fact, does enjoy meat, as long as no-one tells her it is meat she is eating. She is poor and has never been able to afford meat.
FleetCommand
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: 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.
Brad 
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)
Dwarf
The One with the Dozen Lasagnas - S1-E12
Visible crew/equipment: When Ross is on the balcony trying to comfort Rachel after she has split up with Paolo, we see a couple of shots from the balcony looking into Monica's apartment. If you look at the top of the screen you can see where the walls of the set end, and all the stage lights hanging from the ceiling of the studio. (00:18:35)
The One with the Dozen Lasagnas - S1-E12
Visible crew/equipment: When Paulo says goodbye to Phoebe, a boom mic can be seen at the top of the screen bobbing in and out at the top of the pillar. (00:17:45)
Dwarf
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)
Ssiscool The One with the Dozen Lasagnas - S1-E12
Revealing mistake: After Phoebe tells Rachel that Paolo made a pass at her, we see a shot of the outside of Monica's apartment block and Rachel is throwing Paolo's clothes out of the window. Look closely and you can see the clothes have been very badly superimposed on to the background. (00:17:05)
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)
tw_stuart
The One with the Dozen Lasagnas - S1-E12
Visible crew/equipment: When Chandler and Joey are on about buying a table, a line of stage lights is visible in the tv. (00:07:25)
Ssiscool 
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)
Kara
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)
Dwarf
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)
Dwarf
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)
DwarfThe One with the Dozen Lasagnas - S1-E12
Revealing mistake: When Rachel throws Paulo's clothes over the balcony, they land on the corner of the building, yet the balcony isn't near the corner as there are bedrooms between the place where she throws them and the edge of the building. (00:17:15)
DwarfThe 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)
Dwarf
