Inside TikTok, the app for firefighters who enjoy lip-syncing to 'Baby Shark'

Camille Gates' husband would stare at his phone for long stretches of time, laughing at amateur music videos on an app called TikTok. Look, he showed Gates, nurses like her were on TikTok, dancing in their scrubs at work. He persuaded Gates to join.

One week later, the 30-year-old in rural Wisconsin had nearly 50,000 TikTok fans.

TikTok, at its core, is an app for creating and sharing short videos set to music. Lip-syncing and dancing are pretty popular genres. Most creators jump on to viral "challenges," emote over famous monologues from movies and TV or produce clever illusions through editing.

Last month, TikTok was downloaded in the United States more than 6 million times. Its predecessor, Musical.ly, was where 13-year-old aspiring internet celebrities created and exhausted memes before the old people caught on. But something funny happened after TikTok's Chinese parent company bought Musical.ly this year and merged them: Police officers, people serving in the military, mechanics and Walmart employees joined in. Fall into one of these occupational niches on TikTok, and you'll feel like you've stumbled into "The Ellen DeGeneres Show" audience: an earnest, nonstop, normcore dance party.

The app cemented this status when lip-sync battle impresario Jimmy Fallon joined it last week, launching the tumbleweed challenge. It's pretty easy: Choose the song that Fallon's show created for the challenge, and then film yourself rolling on the floor like a tumbleweed blowing in the wind. Anyone can do it.

TikTok has become a unique cultural gathering place. It's where teens and tweens define challenges, games and visual style. Simultaneously, it's where, months after those memes are no longer cool, new communities rediscover them and make them their own. It's as if the moms who post inspirational minion memes on Facebook and the stars of Vine's heyday were all finding space on the same app. (Perhaps that's why Facebook has already launched a feature that is, essentially, a TikTok clone.)

On Military TikTok, uniformed personnel are getting thousands of likes for videos lip-syncing to "Baby Shark," a children's earworm that surged into mainstream memery last summer. "The military is such a strong group and it's really tightknit. When something catches it spreads," said Michael Eckert, a Marine who runs a popular fitness TikTok channel. "Being in the military is a really stressful environment. Being able to get away and shed your skin for 15 to 20 seconds and then go back to work keeps our mentality strong."

"Baby Shark" is also pretty popular with TikTok's firefighters. The #ThinBlueLine hashtag is full of videos from law enforcement, and has more than 37 million views. One of the more popular memes here is #SnapYourLife, an old Musical.ly meme that involves snapping your fingers to the beat of a song in front of the camera. With each snap, you show another part of your day. Law enforcement officers have revived it, using the meme to show off their uniforms and police vehicles. #ThinBlueLine is also peppered with super-earnest and emotional videos from law enforcement spouses about how proud they are of their husbands and wives.

Nurse TikTok, Gates said, is populated with medical professionals who make their videos on break. Sometimes they use the #SnapYourLife meme to snap themselves into scrubs and sterile clothing. Other repeated tropes are pretty nurse-specific, like a nurse playing a patient pretending to run away while another nurse, holding an injection, chases after them. "Nurses have a funny sense of humor that is maybe different from everyone else. It's how you get through this job," Gates said.

Gates works nights in a hospital delivery ward, which can be crazy busy or crazy slow. After she heard about TikTok from her husband, she showed her co-workers some funny nurse dances.

"We'd been talking about how to do - what's the dance the kids are talking about? The floss," she recalled. One of her co-workers could do the floss. So Gates turned on Train's "Hey Soul Sister" to dance to, and set up her phone to record a video. A line of her co-workers, all in their scrubs, did a short dance in a hospital hallway - ending with the one co-worker who could do the floss, flossing.

"It's a pretty easy app to use. I'm not super-savvy," she said. Gates posted the video, her second TikTok ever, to her account, and forgot about it. That is, until it started blowing up. "One of my co-workers pulled it up and was like, 'Oh my gosh, did you see how many views it has now?' "" Gates said. The video has more than 600,000 likes. She's still not fully convinced that she went "viral" - that's not something she ever had in mind to be.

But #CameronFromWalMart, aka Cameron Campbell, always knew he wanted to be famous. The 24-year-old from an Indiana town learned to dance from watching YouTube videos. He joined Musical.ly in 2015 and would upload short clips of himself dancing - in the yard, in front of the garage, in the living room.

"I got hooked on it, and started making them every single day. I was putting up, like, six a day," Campbell said in an interview.

His videos would get around 5,000 or so views per video. Little changed for years - although Campbell improved at dancing. And then, Campbell got a job at Walmart this year. In the backroom of the store, and still in his uniform, Campbell did his daily routine of dancing in front of a camera. Those videos, tagged #CameronFromWalMart, took off, getting hundreds of thousands of likes each. Campbell now has a million TikTok followers.

The uniform, Campbell said, helped him stand out - and it pulled him into the world of retail workers who used the app on their breaks. "When they see someone dance the way that I do, it's like, 'Oh my god, that's just a Walmart guy and he's killing it,'" Campbell said.

Three weeks ago, Campbell quit his job at Walmart. Last week, he auditioned for "America's Got Talent."

TikTok is an endless collection of rabbit holes. Users can swipe from video to video endlessly - the app recommends them based on your viewing history. (It will, after two hours, show you a short note encouraging you to take a break.)

As I reported this story, TikTok began showing me more and more videos of firefighters and police officers, or families making videos together in their homes. Then, I fell into adjacent rabbit holes. Swipe: a grandfatherly plumber in coveralls pausing from fixing a pipe to break into an elegant, entertaining dance. Swipe: a woman, speaking close and directly into the camera, telling her followers to "back off" from her personal life. Swipe: a Fortnite meme. Swipe: a man with his eyes closed, lip-syncing to Christian praise music. Swipe: a teenager coming out as gay.

As TikTok has grown, "cringe" edits have started going viral. Some try to expose TikTok's darker side: sexist reactions to women's videos, or repetition of racist jokes. But more typical is a "TikTok cringe compilation," which has more than 2 million views on YouTube and features clips of clumsy dancing and lip-syncing that doesn't always match up. Presumably, these cringe edits try to make fun of normal people who don't want to win approval of cool kids online and just want to have fun. They reveal the central TikTok divide: What might be a stale meme to a teen influencer at the edge of viral culture can bring someone else joy.

For Gates, TikTok is the one app that makes her happy. She doesn't care for Twitter. And Facebook has become an endless stream of posts that make her frustrated or sad. Gates believes TikTok has the unique potential to spread joy.

"I like that (TikTok) gives people a way to express themselves and peek into other people's lives," Gates said. Scrolling through her video feed, she said, "I'm not getting angry."