1. Central Perk once put a potato in the cake display stand.
2. Following the 9/11 attacks, the show paid tribute to the FDNY and NYPD in multiple episodes.
Submitted by aimeemillerg
3. In "The One With the Jam," you can see someone walking behind Monica's closet.
4. There's a background actor who seems to be chewing her coffee.
5. During Joey's butt double scene, there's a moving box behind the crew that has "Monica's" written on it.
6. The actress who plays Estelle previously played a nurse in the episode where Carol gives birth to Ben.
7. Rachel's last name has an extra "e" in it on her invitation to Ross and Emily's wedding.
8. When Monica is opening her wedding presents, the big box goes from wrapped to unwrapped to wrapped in the span of one scene.
Submitted by Casey Wombough, Facebook
9. When Pete visits Monica at her work, you can see the padding on the floor that's there for when she's supposed to fall down.
Submitted by raysour
10. Just go ahead and look at that little "Reserved" sign on their ~usual~ table.
11. In the 10th season, a giant hole is visible in the wall of Joey's apartment.*
12. In the scene where Chandler is supposed to be wearing only Julia Roberts' character's pink thong, you can see that he's actually wearing boxers or shorts of some kind.
13. When Monica turns to get the wedding ring from Rachel, you can see one of her shoes...which appears to be a comfy slipper of some kind.
14. When Freddie Prinze Jr. played the manny, you can see that the puppets switch hands during takes.
Submitted by e1g3o96
15. The balloons used during Ross's bachelor party seem to be blown-up condoms.
16. Rachel's passport has a picture of some other woman.
17. And finally, Joey and Chandler's door and Monica and Rachel's door go from 4 and 5 to 19 and 20.
Submitted by adens
An earlier version of this post included a moment from "The One With Monica And Chandler's Wedding" where Chandler's office door reads "Mike Smith." The following scene where the joke is explained is not included in the episode available on Netflix.
An earlier version of this post also included a mention of Chandler and Joey’s “second microwave,” which is actually a bread maker.
These items have been removed from the post.