The One Where Heckles Dies - S2-E3
Revealing mistake: After Mr. Heckles has been taken away, in the last wideshot while everyone's still standing in the hallway, when this is viewed on the DVD (Warner Bros. S2 set) we can see a long black line on the floor (as noted in another mistake). The problem is that when this is viewed online on Netflix, even though we can see the very same area of floor, that black line has been blurred out. Weird that it wasn't edited on the DVD, and yet it was for the version available on Netflix.
The One Where Heckles Dies - S2-E3
Visible crew/equipment: When Mr. Heckles is being taken away, just as the officer starts to follow the gurney the shadow of the moving boom mic can be seen on the wall behind him, at the right side of the screen. (Widescreen version).
The One Where Heckles Dies - S2-E3
Visible crew/equipment: Right before Monica breaks the seashell lamp there's a shot of Rachel walking into her bedroom, and just as she walks through the doorway set equipment can be seen at the right side of the screen. (Viewed on widescreen).
The One Where Heckles Dies - S2-E3
Visible crew/equipment: After Mr. Heckles is taken away, when it cuts to Phoebe walking out of the kitchen, the reflection of studio lighting array can be seen on the TV screen. Also later in Heckles' apartment, studio lighting's reflected on his TV screen.
The One Where Heckles Dies - S2-E3
Visible crew/equipment: After Monica yells "Stop with the broom, we're not making noise," when both Monica and Rachel stomp their feet the studio lighting can be seen at the top of the screen, over Ross (this doesn't refer to Monica's star light fixture). And when the others join in stomping their feet, we can also see the boom mic dip into view.
The One Where Heckles Dies - S2-E3
Continuity mistake: After Monica breaks the seashell lamp, when Phoebe says that she wants to believe Monica did it accidentally her right is arm up and points to Monica, but in the next shot it's Phoebe's left arm that's up while still pointing at Monica.
The One Where Heckles Dies - S2-E3
Continuity mistake: After she breaks Rachel's seashell lamp, Monica puts her jacket over the back of the big chair. When Chandler sits on it, the jacket keeps disappearing and reappearing in almost every shot. (00:17:35)
The One Where Heckles Dies - S2-E3
Continuity mistake: When the gang and Mr Treeger watch the paramedics take Mr Heckles away, a thin dark object like a camera mark or a pencil suddenly appears on the floor close to Ross' feet. (00:03:25)
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.