Corrected entry: In the one with Ross and Monica's parents' 35th wedding anniversary, when the parents are talking to Ross and Rachel, there is a picture of the parents in the background, in exactly the same location, wearing exactly the same clothes. That photo would have had to be taken, printed, and blown up in the last hour. (00:05:40)
Corrected entry: When Ross is telling the imaginary story of how he 'proposed' to Rachel, he says that he did it at the planetarium because 'that's where we had our first date.' However this cannot be right because in series 4 'The One with Chandler in a Box,' Ross accuses Rachel of having no sentiment so she shows him a movie stub from their first date, implying that they went to see a movie, not to the planetarium.