Lisa Kudrow is celebrating her 60th birthday!

The actress is best known for portraying Phoebe Buffay for 10 seasons on the hit NBC sitcom "Friends." She appeared on the show alongside co-stars Jennifer Aniston, Matt LeBlanc, David Schwimmer, Matthew Perry and Courteney Cox.

Although the show went off the air almost 20 years ago, it remains as popular as ever, as it continues to find new audiences through its presence on various streaming networks. 

Here are some behind-the-scenes tidbits from one of the most popular shows of the 1990s and early 2000s.

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One of the show's most memorable moments came in the season four finale when Ross mistakenly says Rachel's name at the altar instead of his bride Emily's. Turns out, the storyline was inspired by a real-life mistake made while filming a scene earlier in the season.

In the 2019 book, "Generation Friends: An Inside Look at the Show That Defined a Television Era," Saul Austerlitz interviewed the show's creators, writers, producers and some of the cast. The book contained many behind-the-scenes secrets from the set, one of them being how the writers came up with the idea for the name mix-up.

According to Austerlitz, the writers knew they wanted Ross and Emily to go through with the wedding, but they weren't sure how exactly the episode was going to end. When filming another scene earlier in the season, David Schwimmer, who played Ross on the show, was meant to say "Emily, the taxi's here," but said "Rachel, the taxi's here" instead.

Austerlitz wrote it was "at this moment" when one of the producers, Greg Malins, and one of the creators, David Crane, turned to each other and decided that is how the season would end.

During Max's 2021 special "Friends: The Reunion," the cast and creators of the show discussed how filming a stunt during a particular episode ended with one of the main castmembers injured.

The memorable season three episode, "The One Where No One's Ready," features a running bit in which Matt LeBlanc and Matthew Perry's respective characters, Joey and Chandler, are fighting over who gets to sit in a specific chair. At one point in the episode, both Chandler and Joey run towards the chair, jumping onto it while calling dibs, which is when things went south for LeBlanc.

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"I went just to jump over the coffee table and somehow tripped, and my legs went up in the air and my shoulder came out of the socket," LeBlanc told his castmates during the reunion. The cast later watched footage of the incident, in which LeBlanc can be seen landing on the armchair at a strange angle and walking off, very clearly in pain. 

According to the cast, paramedics were then called onto set and production on that specific episode was shut down. Turns out, LeBlanc had dislocated his shoulder and had to wear a sling, something which was written into the show, explained away by saying Joey fell off the bed.

Prior to landing the role of Phoebe Buffay on "Friends," Lisa Kudrow played the character of Ursula on another popular NBC sitcom, "Mad About You." Ursula was the rude waitress who worked at the restaurant the main characters Paul and Jamie often frequented. Since both shows took place in New York and aired on NBC, the "Friends" writers wrote Ursula into the show.

"My husband Jeffrey [Klarik] was on "Mad About You" as a writer. We had to go to [creators] Danny Jacobson and Paul Reiser to get their permission, and amazingly because of that relationship… they were incredibly generous and let us do it, which is nuts," creator David Crane told Entertainment Weekly in 2019. "I wouldn't let anybody do that with a character on our show!"

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Filming the scenes involved using a stand-in for Kudrow to act across, which ended up being the actress' sister.

"I think feeling the [stress] she put her sister into by being the double was more in her head at the time, so those scenes were a little bit tricky to shoot," executive producer Kevin S. Bright explained. "But it ended up being a lot of fun when you put it together."

At the end of season one, Jennifer Aniston debuted "The Rachel," which would go on to become one of the most talked about hairstyles in the history of television. She continued to sport the haircut throughout the show's second season, but Aniston wasn't a fan of the style.

Aniston has spoken out about how much she disliked the haircut on more than a few occasions. 

"I love Chris, and he's the bane of my existence at the same time because he started that damn Rachel, which was not my best look," she told Allure in 2011. "How do I say this? I think it was the ugliest haircut I've ever seen."

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In 2013, Aniston told Marie Claire that "'The Rachel' was high maintenance."

"I got that haircut and was like, ‘Wow, this is amazing,’ and then I was totally left with this frizzy mop on my head, because I had no idea how to do what he did," she later said at the 2018 InStyle Awards.

In Matthew Perry's memoir, "Friends, Lovers and the Big Terrible Thing," the actor spoke out about the history-making negotiation between the cast and executives. Perry recalled David Schwimmer receiving a lot of positive attention following the first season, revealing it was his idea to negotiate salaries as a team.

"It was a decision that proved to be extremely lucrative down the line," Perry wrote. "His decision served to make us take care of each other through what turned out to be a myriad of stressful network negotiations, and it gave us a tremendous amount of power."

He wrote that by season eight, the entire cast was making $1 million per episode. Perry thanked Schwimmer in his book for "making us stick together when he could have gone it alone and profited more than all the rest."

At the time, People reported, both Schwimmer and Jennifer Aniston took a pay cut in order to make sure the whole cast was paid equally. Aniston spoke about her decision to negotiate as a team during a 2021 interview on "The Howard Stern Show," explaining "we were all doing the exact same amount of work," and that she "wouldn't have felt comfortable knowing [she] was making more."

"We all felt that way," Courteney Cox added. "I thought it was the most important thing — as we all did — that we all were equal in every single way. That was the first time that people had all stuck together in a cast. I think it was scary, probably, for productions after that."

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When the Rembrandts were first approached to write the theme song for "Friends," they were asked by the creators of the show to come up with something similar to a song by the band R.E.M. During an interview with Buzzfeed News, band members Danny Wilde and Phil Solem explained they sat down with composer Michael Skloff and lyricist Allee Willis one day, and two days later were in the recording studio.

"That's where we hashed out the idea and made sure all the parts work," Solem said. "Allee was sending faxes with the lyrics on them, like, 'Here's a new line!' 'Try this one!' 'How about this?' At the end of the day, we had a rough version… So, it was over the course of three days that we were actually working on it. And then, what seemed like five seconds later, it was on TV." 

The song's signature four claps were added in as a final touch, and in an effort to have a hand in the creation of the song, show creators Kevin Bright, Marta Kauffman and David Crane wanted to record the claps themselves. Wilde recalled having to do over 25 takes to get the clapping right.

Initially, the song was only written as a 45-second tune to use for the show's intro. After a Nashville radio station played the song on a loop for three minutes, Wilde explained "it got a crazy amount of requests," prompting them to write the rest of the song.

"Here's what was really crazy: At that point, the producers got in on the writing. So we all just sat around, tossing ideas around," Solem said. "There was a lot of interaction. It was, like, seven people!"

When the full version of the song was released, the cast of "Friends" was featured in the music video.

In his recent memoir, Matthew Perry discussed his addiction to both alcohol and prescription medication, admitting during an interview with Diane Sawyer that he took 55 Vicodin a day, as well as taking Methadone, Xanax and drinking copious amounts of vodka each day.

"You can track the trajectory for my addiction if you gauge my weight from season to season," Perry wrote in his memoir. "When I’m carrying weight, it’s alcohol; when I’m skinny, it’s pills; when I have a goatee, it’s a lot of pills."

While Perry said all five of his "Friends" castmates attempted to help him behind the scenes, he explained that Jennifer Aniston was the one who called him out on his alcohol abuse a few times. He wrote she came up to him and said, "We know you're drinking," and recalled the moment when speaking to Sawyer, saying, "Yeah, imagine how scary a moment that was."

Perry went on to acknowledge Aniston as "the one who reached out the most," adding, "I'm really grateful to her for that."