Visible crew/equipment: After the anniversary party, when Rachel and Ross are back at the apartment and Ross tells her that it was the easiest four hundred bucks he ever made, Rachel gets up and just as she walks around the couch we can see the reflection of the cameraman/crew member in the mirror on the wall, at the right side of the screen.
Character mistake: In the early years, the gang are talking about their pets dying and their parents saying they sent them to a farm and Ross thinks that actually exists. He said that they sent their dog Chee Chee there and HE could run about chasing animals. Then in TOI Massapequa, Monica is preparing her speech and she tells Chandler about Chee Chee and said SHE died when Monica was in school, and when Parker asks whose dog it is, Monica says HE's my old dog. Then during her speech, Monica says HER and Nana are gone. (00:15:30)
Continuity mistake: In The One In Massapequa, Jack Gellar is eating food off a stick. When he finishes he holds the stick while Rachel asks Jack if he has any pearls of wisdom. We can see the stick over Judy's shoulder. In the next shot the stick is gone from his hand, then we see Judy put it down on a table, then it reappears in his hand, before disappearing for good. (00:05:05)