When Chandler is on Ross's back and being dragged forward, Ross reaches for the door handle and opens the door, the camera angle changes, the door is closed and Ross opens it again.
When Joey and Kate are talking for the first time, Joey is holding a mug. Between shots, sometimes he is holding the mug by the handle and sometimes by the mug, with the handle sticking out.
When Joey and Kate are talking for the first time, a man walks behind Joey and sets down a chair. In the next shot it is gone, and then it is back again.
When Mark is telling Rachel they should get back at Ross right there on the couch, Rachel's hands go in a instant from on her chest to down her sides.
When Monica says, "I just recently got out of a serious relationship," she is holding her glass in her left hand. The camera cuts to Pete and the glass is now in her right hand. It then switches back to her left hand in the next wide shot.
Joey enters Monica's apartment singing and dancing, before Ross realizes "he must have got the part in that play". The words Joey is mouthing during this scene are not the same as the ones he is heard singing.
When Joey dances through the kitchen singing "Oh mommy, oh daddy, I am a big old baddie!" his mouth is not moving as he exits Monica and Rachel's apartment.
When Ross and Rachel are arguing about the shirt in the living room, you can see a person in the reflection of the TV that is standing in the kitchen. When Ross then walks out wearing the shirt, there is no one in the kitchen.
During the argument over the "Relax" t-shirt, Rachel reminds Ross that he hasn't worn the shirt since he was 15. Since Ross' year of birth is 1967, this would mean that he owned the t-shirt in 1982, which is impossible since these shirts were not released until 1984.
Kate makes a derisive comment about Joey being a soap opera actor. However, in "The One with the Screamer," Kate leaves the play so she can take a soap opera job.
When Monica returns from her date with Pete, Ross refers to Pete as "Mr. Millionaire" when Pete is actually a billionaire.