The One After the Superbowl, part 2 - S2-E13
Visible crew/equipment: When Joey walks into the bathroom and starts whistling, the shadows of the camera and a passing crew member can be seen on the door of Chandler's cubicle, then the camera's shadow moves as Joey walks toward Chandler and also when Joey's about to stand on the toilet.
The One After the Superbowl, part 2 - S2-E13
Revealing mistake: Rachel grabs a jar of sauce from the shelf and says, "You give me back my sweater or it's handbag marinara." You can tell from the sound it makes when it opens - no pop - that the jar had already been opened before she pulls the lid off.
The One With The Prom Video - S2-E14
Continuity mistake: The prom video has just ended and the TV screen goes blank. Monica had been sitting next to Rachel, but in the reflection of the TV screen you can see her beginning to stand up. We cut back to a 'real' view, and she's sitting down; then she stands up again. (00:20:25)
The One With The Prom Video - S2-E14
Visible crew/equipment: During the prom video, Monica, Rachel, and Monica's date Roy are standing in the living room. When Roy leaves the room saying, "I'm gonna kick Chip's ass," the camera follows him out, but as it's turning the boom mic operator is visible. He's kneeling on the floor sliding the mic toward the girls. (00:20:45)
The One With The Prom Video - S2-E14
Continuity mistake: On the actual prom video tape, it only takes Ross a mere 12-13 seconds to run up the stairs, completely change outfits into his Dad's tux, and reappear ready-to-go on the stairway. This is impossibly fast. Also, it is not possible that the prom video tape was stopped and re-started during this time, which could account for the short duration. The reason is because Ross's mom was the one filming at this point. It turns out that she has no idea how to stop the video recorder. Thus, the video tape was one continuous recording, and we are expected to believe that Ross could change outfits within 12 seconds. (00:21:25)
The One With The Prom Video - S2-E14
Visible crew/equipment: After Chandler throws the basketball and breaks the lamp, in the next shot of Joey as he mentions the bracelet, we can see the reflection of a crew member (standing behind the foosball table) on the left side of the TV screen (Chandler's reflection is at the center of the screen).
The One With The Prom Video - S2-E14
Continuity mistake: When Chandler throws the basketball and breaks the lamp, the base falls onto the chair with the shade, but when Joey walks into his room the lamp base is back up on the desk.
The One Where Ross and Rachel...You Know - S2-E15
Visible crew/equipment: When Rachel's talking about when Richard kissed her when she was a little girl, you can see the boom mic above her head. (00:16:10)
The One Where Ross and Rachel...You Know - S2-E15
Visible crew/equipment: At the start, when Chandler and Joey sink into their new Barcaloungers and proceed to recline, the camera can be seen at the right side of the screen. This can also be seen in the show's intro in later episodes. Additionally, set lighting was reflected on the TV screen earlier when Chandler had mentioned "Green Acres."
The One Where Ross and Rachel...You Know - S2-E15
Visible crew/equipment: While "The Dick Van Dyke Show" is playing on TV, when Rachel walks in and heads over to Ross, a crew member can be seen at the left side of the screen, behind Phoebe.
The One Where Ross and Rachel...You Know - S2-E15
Visible crew/equipment: While Ross is trying to fix the position of the cavemen in the museum, a boom mic can be seen above his head.
The One Where Ross and Rachel...You Know - S2-E15
Plot hole: Rachel says she didn't want to wear her glasses on their first date. Rachel doesn't wear glasses.
The One Where Joey Moves Out - S2-E16
Visible crew/equipment: When Monica, Richard, and Ross arrive at the party, the boom mike is seen at the top of the screen. (00:03:50)
The One Where Joey Moves Out - S2-E16
Continuity mistake: When Joey and Chandler are at Joey's colleague's brunch, you can see a big wall clock in some shots. You can see it when Chandler says: "Wow, there's my fantasy's come true" with the minute hand at five to the hour. Just a few seconds later, when Joey says: "Can you see me in a place like this?" it can be seen when Chandler is in shot, and the minute hand is now at 20 to the hour. (00:05:40)
The One Where Joey Moves Out - S2-E16
Revealing mistake: When Chandler and Joey are arguing, they go into their rooms and slam the doors. By Chandler's door, you can see the wall move. (00:10:35)
The One Where Joey Moves Out - S2-E16
Other mistake: When Rachel is showing Phoebe her heart tattoo, the tattoo isn't dressed and covered, nor is the skin around it red or swollen, despite the fact she just finished getting it. (00:14:09)
The One Where Eddie Moves In - S2-E17
Visible crew/equipment: In the scene where Monica, Joey, and Phoebe are sat on the couch in the coffee house, (whilst the camera is drifting left) a boom mic at the top of the screen is visible for a short period of time. During this time the mic can be seen moving. (00:06:50)
The One Where Eddie Moves In - S2-E17
Continuity mistake: In the previous episode, Joey tells Chandler that the bathroom in his new apartment has mirrors on both sides of the toilet. But in this episode, when we see the toilet from the side while Joey gives the gang a tour, it is clear that the wall is devoid of mirrors.
The One Where Dr. Ramoray Dies - S2-E18
Visible crew/equipment: When Chandler and Eddie are sitting in their apartment getting to know each other, there is a visible microphone in the right upper corner. (00:03:45)
The One Where Dr. Ramoray Dies - S2-E18
Continuity mistake: When Monica is trying to cheer Joey up, she tells him that she straightened out his shower curtain so it wouldn't get mildew. But in a previous episode (The One Where Eddie Moves In), Joey gives the gang a tour of his new apartment; the shower is clearly visible in the bathroom, and it has a door. (00:18:10)
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.