The One With Ross's Teeth - S6-E8
Character mistake: While on his date with Hillary, Ross says that he has a five year old son. Ben was born in 1995 and this episode is set in 1999, so Ben should be four, not five.
Starring: Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matthew Perry, David Schwimmer, Matt LeBlanc
The One With Ross's Teeth - S6-E8
Character mistake: While on his date with Hillary, Ross says that he has a five year old son. Ben was born in 1995 and this episode is set in 1999, so Ben should be four, not five.

The One Where Phoebe Runs - S6-E7
Visible crew/equipment: When Phoebe bends over to tie her shoelace before the first run, and later when she surprises Rachel at the park while running, the mic pack bulge under Phoebe's top can be seen on her back, and when Rachel bends over there's a bulge at her back as well. It's also a bit noticeable the third time they run.
The One With Ross's Teeth - S6-E8
Monica: What happened to your teeth?
Ross: I whitened them.
Chandler: Really?
Ross: Yeah, what... What do you think?
Monica: Well, uh, I think I shouldn't look directly at them.
Ross: Come on, seriously.
Monica: Ross, they're really, really, really white!
Chandler: Yeah, what was wrong with your old... Human teeth?
Ross: Well, I did leave the gel on a little longer than it said to.
Monica: How much longer?
Ross: Uh, uh... A day.
Monica: Ross, you know that tonight is your date with Hillary?
Ross: I know! That's why I did it! Come on, are they really that bad?
Chandler: No. No, no, no, you'll be fine. Hilary's blind, right?
Monica: She will be after tonight.
The One With The Prom Video - S2-E14
Trivia: The first day Courteney Cox donned the 'Fat Monica' make-up and costume, Matthew Perry walked right past her without recognizing who she was.
The One With the Sharks - S9-E4
Question: What's the name of the "scary painting" that Joey saw in the apartment of the girl he thought he'd slept with before? The strange and creepy painting (black and white, with an amorphous body and a chair). I really, really want to know who is the artist. Not Gladys - that's Phoebe's painting that comes out of the frame.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.