The episode aired exactly five years before the series finale. Numerically, this episode also marks the halfway point in the series, being the 118th out of the 236 episodes.
Incorrect Goof: Hairless cats are not actually hypoallergenic. Monica could have had an allergic reaction to it. Dander is what usually causes allergies. Dander comes from skin, not fur.
(episode #5.21), Chandler visits Phoebe's boyfriend Gary (Michael Rapaport) at his precinct. When they sit at Gary's desk, a blackboard with names written in blue chalk is prominent behind his head. All of the names on the blackboard are references to or characters from the films of Stanley Kubrick (Alex, Dim, Hal, Kissoff, even Redrum).
David Schwimmer is actually allergic to cats.
In the uncut DVD version of the episode, Rachel is also shown throwing the ball. Ross also wakes up and says he dreamt that he was "drowning and not throwing this ball".