It isn't clear if this is because Jennifer Aniston was busy with different projects, but it turns out that in a scene in the ninth season of the hit TV series Friends, another actress played the role of Rachel Green.
Did you notice that Aniston briefly disappeared in the season's episode 15?
A keen-eyed fan of the show spotted a mystery woman, who wasn't part of the cast, playing Rachel Green - something many fans admitted they never noticed, even if they were on their 203rd marathon of the series.
In season 9, episode 15, "The One With The Mugging," Aniston was replaced.
This discovery was made by a fan in 2015 and was published on the website recentlyheard.com in an article about the series.
You can't fool a #Friends fanatic. Why is this not-Rachel standing in for Rachel in this ep? https://t.co/7U8K9VAhl4 pic.twitter.com/drO44q9qax— Decider (@decider) November 12, 2015
In this episode, Rachel ran to the apartment of Monica Geller (Courtney Cox) to tell Joey (Matt LeBlanc) that he can audition for a Broadway play directed by actor Leonard Hayes (played by Jeff Goldblum).
However, when the camera cuts back to Joey, we see Rachel standing next to him - but she clearly isn't Jennifer Aniston.
How many times has Friends replaced its actors in scenes?
But this isn't an isolated incident. The same thing also happened to Monica in season eight, episode five, "The One With Rachel's Date." There, another actress replaced Courtney Cox. It was just for a second and a half, but the fans were able to notice.
This isn't even unprecedented with Jennifer Aniston. As reported in the UK media outlet The Independnet, the same thing happened in season nine, episode four, "The One With The Sharks," where someone else replaces Aniston as Rachel in the middle of the scene.
Around the 13th minute of the episode, Monica and Rachel - with a yellow shirt and curley hair - are seen sitting in their apartmnet when Joey comes in. When the camera pans to Monica, we can see a different woman sitting next to her who has straight hair and a blue shirt.
Although some of these mistakes have been spotted over the years, many more have been spotted ever since Friends hit Netflix, since now fans can watch it in HD.
In addition, the show was originally broadcast in 4:3 ratio. However, for Netflix, it has been adapted to 16:9, which means that things that were once out of frame in the original broadcast can now be seen.