The Magna Doodle in Joey and Rachel's apartment has a sketch of the Statue of Liberty and the letters 'FDNY', in reference to the September 11 attacks and the firefighters of New York.
In this episode in many scenes you will see a flag, "FDNY" and "NYPD" hats etc. In rememberance of 9/11
RE-CAST: the role of 'Dina Tribbiani' was originally played by Lisa Melilli in season 3.
In the scene where Phoebe is talking to Ross about the concert tickets, when she starts to sing, you can see Jennifer Aniston and Courtney Cox break character and start laughing.