Phoebe's snack keeps changing in size and switching between two hands when the group is discussing about money issue at the restaurant.
In The One Where Heckles Dies (1995), Monica says she's allergic to seafood. In this one she orders the prawns, a type of seafood.
She was lying to get Rachel to get rid of the lamp.
When Monica runs into "Little Stevie Fisher" it makes no sense that she could have been the babysitter of a kid who has been to law school. She is in her mid-20's at the beginning of the show, so at best, she would have been the same age as a kid who has been to law school.
Jade says that she's the legs on the new Bond Poster. There were no legs on the poster for GoldenEye (1995), and the tradition seems to have stopped since The Living Daylights (1987).
In the restaurant Ross divided sum of the bill incorrectly - each should pay $33.60, not $33.50.
However, as the total bill amount was not stated, it's likely that Ross rounded the shares to the nearest half dollar rather than calculating the amounts exactly.
When Monica is on the phone getting terminated she is using the left ear using a left hand but in the next shot she is on the right ear using the right hand.
When Rachel is on the couch talking about how Chandler, Ross, and Monica don't understand that they - Rachel, Joey, Phoebe - don't make as much money as they do, and the shot switches to include everyone, a boom mic is visible twice at the top of the screen above Joey.
It's quite impossible that Jade (a woman, who called Joey and Chandler's apartment) didn't find out that person who answered the phone is not Bob. Even if Chandler knew Bob well, it should be suspicious to her that there is another voice (Joey's) on the answering machine message.