Yet another example of how this sitcom, like so many others, not only depicts characters casually walking into each other's unlocked apartments, but is actually a line of dialogue that depends on it: Monica, upset that Phoebe thinks the initial "hot spark stage" of Monica and Chandler's relationship has ended, asks her at Central Perk about Phoebe and Gary's activities, and when Phoebe inquires as to why Monica was asking, Monica says she just wanted to know what they were doing so that Phoebe didn't accidentally walk in on her and Chandler in the throes of passion. Well, how could Phoebe, who doesn't live at that apartment, "accidentally walk in" on them? Do Chandler and Monica not only not lock their apartment door but their bedroom door as well? This silly. It's like this show exists in some bizarre parallel universe (not to be confused with the Hot Girl Parallel Universe that Joey posits in this very episode) where a couple engaged in private activity don't have the ability to just ignore people who buzz their apartment or knock on their apartment door. Indeed, later on in the ep, Joey walks right in on Chandler and Monica as they recline on the living room sofa, albeit it's after they've had sex, and are covered with sheets or clothing.