As with all shows that end up running for the length of 10 seasons, continuity issues begin to arise when you start to incorporate flashback episodes, references to characters' pasts, or one-off jokes that seem hilarious at the time but actually create glaring issues in the series' timeline. Sure, it's presumably somebody's job to check this stuff, but you can't read a hundred scripts before shooting every episode, can you?

That's to say, none of this stuff really matters, but isn't it fun to comb through a show to find a whole bunch of continuity mistakes anyway? We'll answer that for you: absolutely.

Friends, of course, remains one of the most beloved TV sitcoms of all-time, which is made more impressive by the fact that it's the only show from over a decade ago that everyone still seems to be watching on a constant, almost mind-numbing loop. Oh, syndication.

Thankfully, the show is still genuinely hilarious. With so many repeats, though, and having been exposed to each individual episode say, oh, six hundred times each, it's becoming easier to spot those times when continuity takes a little holiday.

Let's cast our minds back to those instances where Friends done goofed, then, shall we?

17. Monica's Apartment Changes Numbers

Did Monica's apartment fall through a vortex and wind up in another dimension or something? Nope: the writers realised that it made no sense that the number 5 would denote an apartment on an upper level floor level in a large block and switched it around for 20 instead - all without telling us about it!

As a result, Chandler's apartment also made a shift from 4 to 19. Nothing wrong with this, of course, given the logic behind the change, though it probably proved itself to be something of a nightmare for New York postal workers.

16. None Of The Friends Know How Old They Are

The ages of the Friends change depending on who's talking to who, and what joke punchline the writers need to reinforce at any given time. That's to say, no character in Friends has a consistent age.

In "The One Where They're Going To The Party," for example, Joey states that all three of the boys are the same age - 29. In "The One With The Birth," though, Monica says she's 26 and Joey is 25. But isn't Ross Monica's older brother?! WHY DON'T YOU KNOW HOW OLD YOU ARE, GUYS?