The role Vine played in creating the musical and sound library for a decade of memes that followed the end of the app is undeniable.

Sound effects like the ubiquitous "Vine Boom" or "Bruh" sound effects were popularized on the short-form video sharing app, which played a pivotal role in pioneering the short video formula on mobile apps during the early 2010s.

One such sound effect is that of a little kid standing in a dimly lit room in shades evocative of 2016's Oscar Winner Moonlight, answering the question, "What's 9+10?" with "21" in a cadence that puts "Burger King Foot Lettuce" to shame.

So, what's the classic "21 meme" all about, and where did it originate online? Here's how the clip became a meme staple over the course of the decade that followed.

Where Does The '9 + 10 = 21' Video Come From?

Viner @DREHUPEMSU @WESTROSECRAN posted the original "9 + 10 = 21" video on June 22nd, 2013, showing a little kid standing in a dark room, one side of his face bathed in a dark blue light, a bright yellow door standing in contrast behind him. The person recording the video, possibly the kid's brother, tries to aggravate him by saying, "You're stupid," to which the kid replies, "No I'm not."

The person recording then asks, "What's 9 + 10 then?" The boy takes a beat to answer, replying with "21," only to receive another "You stupid."

The Vine gathered over 30 million loops and 700,000 likes before Vine was taken down, numbers unheard of for a short video platform before Vine.

How Did The 'Twenty-One' Become A Meme?

Vine remixes that featured the "21" sound effects began to go viral after 2014, with YouTube reposts gathering millions of views.

By 2016, the thus-far unidentified boy even became the subject of a runaway hoax, with a satire website posting an article about how the young kid ran away from home, only leaving behind a note that read, "I tired of everyone lafing(laughing) at me, I running away forever now, if yu(you) want to find me the only clue I leaving is 21."

Did The '21' Meme Ever Have A Resurgence?

The 21 Kid meme saw a brief resurgence in 2019, primarily in the form of meme edits and compilations posted to YouTube in the weeks leading up to summer.

In 2021, a Twitter (now X) account began a countdown leading up to September 10th, 2021, joking that it's a day where "9+10 really does equal 21," and that when the day does come, "he will decide your fate."

More meme pages latched onto the joke in the days leading up to September 10th, making dramatic and ominous edits featuring the 21 Kid.

The Instagram pages @spoobydoo and @chronic.memesv2 posted jokes that gathered several thousand likes apiece in early September 2021.

What Are Some More '21' Memes?

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For the full history of 9 + 10 = 21, be sure to check out Know Your Meme's encyclopedia entry for more information.