In the wedding reception, Susan asks Ross if he would like to dance and says that she will let him lead. When they stand up and begin to dance Susan is in the lead position (Left hand up) but when the camera angle changes Ross is in the lead position.
After everyone watches Joey's scene, Joey turns back around to talk. Because he is sitting on the table where Chandler has a glass of milk drink, Joey's knee accidentally hits Chandler's milk and spills it. You can see Ross and Rachel both look down at the spill, then when it cuts to Chandler, see the milk spilled on the table.
When Joey turns around to tell his friends about "smell the fart acting," the T.V. isn't on anymore. However, when they turn back around to keep watching, the T.V. is back on.
When Ross & Chandler go to leave the apartment, Phoebe is standing at the door. She walks in, and you can hear Ross close the door, but you can see the door is still open a bit.
When the preacher says "nothing makes god happier," the camera switches angles, and before it does, her lips are clearly not moving but her voice is saying the words.
At Carol and Susan's wedding, as Ross walks Carol in, you can hear the violinist accidentally brush the violin strings with the bow. The music itself was either played back from a tape or added in post production.
When Ross gets up to shake Rachel's mom's hand in Central Perk, the edge of the set is visible to the left of him where the crew can be seen watching a screen. [Only visible in the 16:9 widescreen version. The original 4:3 TV version was cropped to avoid these issues]
As with all the work-centered story lines concerning Joey playing Dr. Drake Ramoray on "Days Of Our Lives", that soap opera films in California, yet Joey and his friends are living in NYC.
After Joey says "smell the fart acting," the cast messed this scene up several times because they kept laughing. But the editors didn't completely cut it out, so right after Joey says it, you can see Jennifer Aniston start to laugh before it goes to the next shot.
At the beginning of the episode when Carol & Susan pick up Ben and tell Ross that they are getting married, "Ben" is changed out to a baby with darker hair.