Jane Sibbett is clearly pregnant, but this was not acknowledged or worked into the storyline.
In the scene when Ross and Ben play the prank on Rachel because Jennifer Aniston didn't know what was happening she freaked out when the dummy came down the stairs. The scene ends with her scream but in extended scenes she screams David not Ross.
The Magna Doodle has a seesaw with a little boy on one end and what looks like a bunny rabbit on the other.
In the imaginary tag scene where a fat Joey is married to Monica, Joey raises some food to his mouth on a fork but just holds it there as the credits roll. It suggests that all the "fried stuff with cheese" is actually inedible prop food. In any other scenes involving eating, the actors actually eat, even when there are multiple takes involved.
In the scene where Chandler and Monica are in bed together, they agree that they "weren't that good friends anyway." In The One with Ross's Tan (2003) when Rachel and Joey decide that their relationship is hopeless, they agree that "Monica and Chandler weren't as good friends as we are."