In this episode, Nina says that WENUS stands for "Weekly Estimated Net Usage Statistics". In the previous episode, Chandler explains that it stands for "Weekly Estimated Net Usage Systems".
When Ross is leaving to go to Lamaze class, he puts on Monica's jacket twice (once when the camera is on Rachel, and you can see him put his right arm in the jacket, and then again when the camera goes back to him, he is again putting his right arm in the jacket).
At around 18 minutes, Rachel is in a leaning position against the back of the Central Perk couch but while Joe stands up and starts talking to Phoebe, Rachel alternates between leaning on the couch and standing straight between shots.
Around 7 minutes and 15 seconds when Joey is talking with Chandler about Ursula likes him, Chandler's water bottle cap keeps on and off between shots.
Jennifer Grant plays a character named Nina Bookbinder in the episode. In the credits, she is erroneously listed as playing a character named Michelle.
At around 13 minutes, when Phoebe is watching TV at Monica's, a woman and a man say "Buenas noches" to each other in the TV program. The subtitle is incorrectly "Buenos noches".
There is no reason for Fran (Leila Kenzie) and Jamie (Helen Hunt) to think Phoebe, who they have mistaken for Ursula, is a waitress at Central Perk. Ursula is a waitress at a completely different restaurant and gives no indication that she is a waitress here where they have happened upon her.