We can’t count on our two hands how many times we’ve seen each and every episode of Friends. We wouldn’t necessarily call ourselves experts on the popular sitcom, but we’ve definitely picked up on a few mistakes that might go unnoticed to the average viewer.

For example, did you know each character had a lookalike stand-in, who would replace the actors during non-speaking scenes and occasionally make unwanted cameos on the show? Keep reading for details on the most obvious Friends mistakes.

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1. The one with the props

Props sound great in theory, but they can sometimes be a burden when improv is the norm. Friends is a victim of several prop mistakes, whether it’s vanishing jewelry or magical soda cans that randomly transform into water bottles at a moment’s notice.

One of the most notable Friends mistakes occurred in season one, episode four (titled “The One with George Stephanopoulos”), when Ross (David Schwimmer), Chandler (Matthew Perry) and Joey (Matt LeBlanc) attend a hockey game. In one scene, Ross is holding a large foam finger. In the next, the prop is MIA as Ross uses both hands to signal his dissatisfaction to the ref. Suspicious, indeed.

2. The one with the quick-change

It’s hard to keep track of every outfit the cast wore throughout all ten seasons, but when a character walks through a door wearing one thing and then emerges donning something completely different, it doesn’t go unnoticed (by us, at least). This happened during season five, episode 17 (titled “The One with Rachel’s Inadvertent Kiss”), when Joey confronts Ross at his apartment. Although he’s wearing a purple zip-up in the hallway, his shirt changes color to black when Ross opens the door.

3. The one with the stand-in

Fun fact: Every main character on Friends had a stand-in, which is pretty self-explanatory. The person would stand in (get it?) when the real actors weren’t needed on set. This is usually done so the big-name celebs don’t have to wait around for hours while the crew tests lighting and camera angles. However, in some scenarios, the stand-in would fill in during actual scenes that are being filmed for TV.

For example, there’s a part in season eight, episode five of Friends (titled “The One with Rachel’s Date”), where Phoebe (Lisa Kudrow) is talking to Monica (Courteney Cox) at Central Perk. The shot is a close-up of Phoebe, showing only the side of Monica’s face. There’s no denying that Cox is there in the beginning, but as the conversation progresses, it’s clear that she gets replaced by someone who resembles Cox…but isn’t her.

The same thing happened in season nine, episode 15 (titled “The One with the Mugging”), when Rachel (Jennifer Aniston) is standing behind Joey’s shoulder. At one point, Aniston is replaced by a lookalike who’s wearing a completely different shirt than her character was.

After ten seasons, there were bound to be some mistakes.

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