At the very end, right after the video of the prom shuts off, you can see in the TV reflection that Monica sits up and is on her knees but when the camera angle changes, Monica has to sit up again? One of many continuity problems throughout the entire season.
I have noticed that before and I think it may already be a slip-up on this site.
But to clarify something. Continuity refers to when something changes from one episode to a later episode. like in Friends when Ross says he doesn't like Ice Cream, but had been seeing eating ice cream at least a couple times over the course of the show prior to that point.
This slipup is an editing error. When they edit multiple takes together, things like that happen.
Editor's Note: Yes, these things are hard to prevent. However, this is defined as continuity. The bigger shows, such as "Seinfeld" and "Friends," actually have a person whose job it is to focus on continuity between takes, camera angles, etc... Their primary focus is to make sure things like this do not happen. Liking ice cream in one episode and not liking it in another is an "inconsistency between episodes" and not classified as a slip-up.
Thanks, Pete