Continuity mistake: When Ross and Cheryl are standing in the hall outside Cheryl's apartment, she's holding her keys in her right hand when she asks Ross if he'd like to come in, but after Ross makes the joke about Homo erectus, Cheryl opens her hand and the keys have vanished from her hand.
Other mistake: When Chandler and Monica are sitting at the table after playing Gin, Chandler's bottle of Yoo-hoo is on the table, but the label reads "Yooh" because the brand name has been partially covered - the blue letters "oo" are yellow to match the background.
Other mistake: When Monica realizes that the cookies were the Nestle Toll House recipe, Monica tosses the yellow bag of Nestle brand chocolate chips to Phoebe, and the brand name has been partially covered so it looks like "I Iest" and the Toll House logo on the side has also been partially covered.
Continuity mistake: When helmet-wearing Vicar Joey taunts Rachel one too many times she turns the tables on him, so when Joey backs away from Rachel he gets pushed up against the front door, and although he can't move, in the shot facing Joey he's at the left side of the door, but in the side shots he's at the right side of the door.
Continuity mistake: After Chandler has written the message on the Magna Doodle, the sliding eraser moves from the right to left side just as he leaves with Monica, and when Joey and Chandler are playing foosball, the barely legible "Joey" is now neatly written on the Magna Doodle, and its sliding eraser is again back to the right side.
Continuity mistake: While Monica and Chandler confront Janine in Joey's apartment, we can see the drawing of the fire breathing dragon and the ape on the Empire State building on the Magna Doodle, then when Joey tells Chandler and Monica to leave because he needs to talk to Janine, the drawing differs - note the dragon's scales, its position, the building, etc.
Continuity mistake: When Ross tells Chandler and Rachel that he's running out to buy name tags for his party, in the next shot the water bottle beside Rachel does not have its cap on, but it cuts to Rachel's closeup and the cap is on. Other differences can be seen as well, such as Rachel's hair and an extra utensil.
Continuity mistake: After Ross announces his tenure, when Rachel starts crying and tells him that she got fired and didn't get the other job, her right hand is up by her face, but in the next shot her right hand is holding the glass of champagne and it's her left hand up by her face.
Continuity mistake: While Mama Joey is looking for Chick Jr. and Duck Jr., the things pinned to the bulletin board beside the door have vanished when Monica and Chandler walk in, but after Monica walks out to check on the twins everything's back up on the board like it was before.