There are actually two major things that Rachel Green fans may not have noticed before, and one was when Jennifer Aniston was straight up replaced in one episode. According to Stylist, if you look carefully in the episode, "The One with the Mugging," you can see a stand-in who is definitely not Aniston next to Joey. It's not uncommon for TV shows and movies to use stand-ins for scenes where an actor isn't in full view, especially if they're busy doing other things. But this mixup is exceptionally funny, because the other actress is not even wearing the same outfit as Aniston was at the beginning of the scene (via YouTube). It's like a Starbucks cup in a "Game of Thrones" episode and feels like they weren't even trying. 

Another Rachel Green specific that fans might not have noticed before is Aniston's particular vocal tick before delivering some of her lines. This was actually discovered by a fan on TikTok (@cts.trphe), who pointed out that the actress often clears her throat before speaking (via the Daily Mirror). Another fan even put together a YouTube video of every time she does it in the series. While some people think it's annoying, others find it to be very realistic acting. Wherever you stand, there's no denying that you won't be able to watch the show without noticing now that you know.