Monica hands the photo of the dog to a guest to give it to her parents. Then the camera changes to Jack and Judy holding the photo and looking at it. However, when the camera turns back to Monica and the guests, the man can be seen on the left just now handing the photo to the Gellers.
When Rachel wraps her gift at Chandler and Monica's apartment, she uses opaque blue ribbon. When she arrives at the party, the gift is wrapped in transparent white ribbon.
When Ross is handed the first check, he can be seen opening it twice.
When Ross and Rachel enter the party and speak with Ross's parents, and Ross says, "We have to pretend that we're married", there is clearly a stand-in for Elliott Gould (Jack Geller), right before Jack says, "I had to shave my ears". The stand-in also wears glasses, while Jack does not.
The same stand-in can also be seen again when Ross stands to give his speech for Jack and Judy's anniversary. Before this, Jack is seen seated beside Judy, but when Ross stands, the same stand-in is seen sitting beside Judy instead.
The same stand-in can also be seen again when Ross stands to give his speech for Jack and Judy's anniversary. Before this, Jack is seen seated beside Judy, but when Ross stands, the same stand-in is seen sitting beside Judy instead.
When Jack Geller says, "Why would you serve food on such a sharp stick?", he can be seen inspecting the stick. When the shot changes to Ross and Rachel, the stick is still visible, and when switched back to Jack and Judy, the stick is suddenly not in Jack's hand.
While Ross is recounting his proposal to Rachel and reaches the point where he says, "The lights came down and I got on one knee," his lips are obviously not synced with the the dialogue heard.
During the anniversary party, while Joey and Phoebe are talking, at one point there is noticeable shaking of the camera that was filming the scene.
At around 20:03, when Ross and Rachel are recollecting their fake marriage proposal and wedding, Rachel stands up, and as the camera pans around her, you can see a crew member in the mirror behind her.
At around 0:04:40, the top 1/10th of the image is black.
When referring to the now-dead dog in the photograph, Monica refers to it as "she", but then minutes later refers to the same dog as "he."
Since Jack and Judy Geller got married because Judy got pregnant with Ross, Ross should be around 34 or 35 years old.
When Ross and Rachel are discussing their fake wedding ceremony, Rachel makes the comment that this may be the only wedding she ever has. But they got married when they were in Vegas, so this fake one would have been her second wedding.
Customarily, money and presents given to the bride and groom are from people who were invited to the wedding ceremony and reception; therefore, Rachel and Ross likely wouldn't have gotten all the money from their family and friends.