Friends is one of the most popular sitcoms ever and took to the screens in the mid-90s, airing on NBC for 10 seasons over 10 years. The series follows the lives of 6 close friends: Chandler Bing, brother and sister Ross and Monica Geller, Rachel Green, Joey Tribbiani, and Phoebe Buffay. All of them are single and in their early 20s, living in New York. Friends' main cast live their lives in relatable ways, struggling through dead-end relationships and careers, but teach fans that one thing is consistent: friendship.

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The 6 friends form an incredibly close-knit group. Old high school friends, Rachel and Monica become roommates with Monica's previous roommate, Phoebe. Chandler and Joey are their neighbors across the hall, and Ross is Monica's brother, who went to college with Chandler. Friends set the scene for a lot of modern sitcoms, but the series wasn't always consistent.

5 Ross' Birthday Occurs In Several Months Of The Year

Ross sits with his arm around Joey's shoulders in an Airplane in Friends.

Ross Geller is the group's kind paleontologist and – like all the main characters – had multiple birthdays over the course of many seasons. Over 10 years, Ross' birthday is mentioned three times, all recounting a different month. In Season 1, when Joey gifts Ross Rangers tickets in October as a birthday present, Ross complains, explaining his birthday was seven months prior. In Season 4, when Gunther asks when his birthday is, Ross says December. Ultimately, fans are left to decide that Ross' birthday is most likely in October, as Ross states that his birthday is October 18th on a medical form.

4 Monica's Age Seems To Differ

Monica Geller, main character in Friends.

Monica Geller's age also seems inconsistent in Friends. Audiences are told in season 1, "The One With The Ick Factor," that Monica is 26-years-old. After previously lying to a potential new partner and telling him she's 22, Monica comes clean and admits that she is 26.

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But in season 7, Monica goes out for drinks with friends from work for her 30th birthday. Much to her surprise, Chandler organized a sophisticated party and invited her parents, and Monica shows up to the surprise party intoxicated. Since the episodes mentioning her age are about 7 seasons apart, Monica should be around 33-years-old by the events of the seventh season.

3 When Did Rachel And Chandler Meet?

Rachel Green and Chandler Bing sit together dejectedly in Friends.

Rachel enters the first season after she flees her wedding day, leaving her fiancé, Barry, at the altar. When the show picks up in episode 1, Chandler is already an important part of the group. According to that episode, Rachel and Chandler meet for the first time in Central Perk, but in flashbacks throughout the series, audiences see Rachel and Chandler meet on two other occasions.

Fans see one meeting in season 3, where Rachel shows off her engagement ring given to her by Barry, but describes her desire to have one more meaningless encounter with a man before she is a married woman. Chandler overhears and tries to get her attention in the bar, which would later become Central Perk. The other time they meet "for the first time" is at Monica's and Ross' family home for Thanksgiving, as the cast look back on their best and worst Thanksgivings throughout the years.

2 Can Chandler Bing Cry?

Split image of Chandler Bing through the series of Friends.

There are lots of running jokes about Chandler's personality scattered throughout the series. The fact he hates dogs, his middle name being Muriel, and his inability to be 'smooth' are just a few fan favorites. In season 6 of Friends, an entire episode is dedicated to Chandler's ongoing inability to cry.

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He points out he is unable to cry at sad films, and the group try to elicit an emotional response from him, eventually deciding that he feels no emotions. That said, Chandler already cried in season 4. After season 6, he cried even more, probably because of this episode's events helping him get more in touch with his emotions. And of course, he bawled when Monica agreed to marry him.

1 Monica's Famous Door Number Changes Through Seasons

Monica's stands next to her apartment door in Friends

Monica's apartment in Friends is iconic, as so many of the episodes revolve around this setting. During the first season, Monica's apartment number changes from 5 to 20. If Monica's apartment number changed, Chandler and Joey's apartment number must have changed too, from number 4 to number 19.

This is apparently because of the height of the apartments. Since they are one of the top floors, it doesn't make sense for their numbers to be so low. It's much easier to spot inconsistencies now that Friends is streaming on Netflix. Now that viewers don't have to wait a week between episodes, anyone can binge the entire 10 season sitcom and keep an eagle-eye open for flaws and plot holes.

NEXT: Friends: 10 Episodes Where Monica Shows Off Her Competitive Side