Read the original article on Best Life. You don’t even have to be watching very closely to see it. In the Season 8 episode, “The One With Rachel’s Date,” Phoebe (Lisa Kudrow) has a conversation with Monica (Courteney Cox) at Central Perk—only…that’s not always Monica. At about six minutes and 23 seconds into the episode, you can see that Cox has been replaced by another woman. In the next shot, she’s back. For more ’90s nostalgia sent right to your inbox, sign up for our daily newsletter. The same snafu happens in the Season 9 episode, “The One With the Mugging.” Blink and you’ll miss it, but at about the three-minute-and-13-second mark, when Joey (Matt LeBlanc) is excitedly telling Rachel and Monica about an audition he just scored, Jennifer Aniston is briefly replaced. The mistake isn’t quite as blatant as the one in Season 8, but it’s definitely there (for you). To find out how the show could have been cast, check out This Star Almost Played Jennifer Aniston’s “Friends” Role. The two women who’ve snuck into these frames are the actors’ stand-ins, a job that’s exactly what it sounds like. These professionals take the place of actors so shots can be set up. Basically, they make it so that the actor isn’t needed on set and that production can keep moving. In the case of Friends, which was shot in front of an audience, stand-ins were used when a character wasn’t meant to be on camera even though they were present in the scene. Having a stand-in take her place likely meant that Aniston could take a break or do a wardrobe change while filming went on. For more TV errors that will blow your mind, check out The Major Mistake in the First Episode of “The Office” You Never Noticed. As Refinery29 explains, the aspect ratio (the width and height of the frame) of Friends is different now that it’s on streaming than it was when it first aired on TV. While it was originally meant to be seen in a standard aspect ratio, you’re now watching it in widescreen. Therefore, you’re seeing a lot of detail outside of that standard frame that viewers didn’t see when they were watching a brand-new broadcast Friends episode on NBC back in the ’90s. And that includes stand-ins, who were meant to be just outside of frame. So look at it this way: you’re not seeing a mistake so much as your seeing exactly how your favorite TV show was made. For more nostalgia from the decade, check out ’90s Celebrity Couples You Totally Forgot About.ae0fcc31ae342fd3a1346ebb1f342fcb