Your News Feed is about to get a lot more expressive. After months of user testing in a handful of countries, Facebook today is releasing "Reactions" to the rest of the world. The feature isn’t so much a new tool as it is an extension of an existing one; by long-pressing—or, on a computer, hovering—over the "like" button, users can now access five additional animated emoji with which to express themselves. Each emotive icon is named for the reaction it's meant to convey. "Like" you already know—say hello to "love," "haha," "wow," "sad," and "angry".

The mission to build Reactions began just over a year ago. Mark Zuckerberg had finally conceded that the platform needed a more nuanced way for users to interact with posts, for the obvious reason that not every post is likable. “Mark gathered a bunch of people in a room and was like, 'hey we’ve been hearing this feedback from people for a really, really long time,'” recalls Julie Zhuo, a product design director at Facebook who worked on the reactions product. At the time, users had the option to post a sticker or—gasp—leave a written comment on a friend’s story. But in December of 2015, 1.44 billion people accessed Facebook on mobile. Of people who access it on both a monthly and daily basis, 90 percent of them do so via a mobile device. Commenting might afford nuanced responses, but composing those responses on a keypad takes too much time. People needed a way to leave feedback that was quick, easy, and gesture-based, says Zhuo. Emoji, it seemed, were the best option.

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Emoji are more than playful shorthand for the written word. Nearly 70 percent of meaning derived from spoken language comes from nonverbal cues like body language and facial expression, says Vyvyan Evans,a professor of linguistics at Bangor University who studies the use of emoji in communication. “The stratospheric rise of emoji," in text messaging, on Facebook, and elsewhere, he says, "is essentially fulfilling the function of nonverbal cues in spoken communication." The challenge for Facebook was deciding which emoji to use. There are hundreds to choose from, but Zhuo and the design team wanted to keep users' options limited. Too many choices would make the Reactions feature unwieldy. “It was really important that we made the thing people do billions of times a day [i.e. like a post], not any harder,” Zhuo says.

Distilling the vast range of human emotions into a single row of emoji is no simple design problem, so Zhuo and the team enlisted the help of Dacher Keltner, a professor of social psychology at UC Berkeley. Keltner was a science consultant on Pixar's *Inside Out * and had worked with Facebook previously to develop stickers, a precursor to Reactions that Facebook brought to Messenger in 2014. Keltner told Zhuo's team that, to fully capture the complexity of human emotion, Facebook would need to include 20 to 25 different reaction emoji—enough to convey everything from fear to desire to relief. "But then you know, you're constrained by engineering" says Keltner; 20 emoji, in other words, was too many.

And Then There Were Six

Facebook decided to focus on the sentiments its users expressed most often. Zhuo and the team began by analyzing how a subset of Facebook users from around the world used the platform. They looked at the most frequently used stickers, emoji, and one-word comments and found a few common emotional threads amidst an ocean of diverse sentiments. “When we built the stickers for Facebook the most common thing people sent was love,” Keltner says. People used the hearts-in-the-eyes emoji more than any other. They were also prone to expressing humor, sadness, and shock through visual means. The team took a subset of reactions that cut across the emotional spectrum and removed redundancies like sympathy and sadness, and joy and love. Then they tested them with users.

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Geoff Teehan, another design director at Facebook, explains that Reactions needed to fulfill two main criteria: universality and expressivity. Because emoji are nonverbal in nature, there couldn’t be ambiguity about what any of them meant meant in different cultures. Originally, Facebook included “yay” in their set of reactions. The grinning face looked happy; it was certainly an emoji that conveyed a sense of “yay.” Keltner himself says he was a major proponent of the celebratory emoji. "It's such a good human reaction," he says. But yay also conveyed a handful of other positive emotions like “love” or even “haha.” “People actually ended up using that one less than all the other reactions,” Zhuo says. “It sort of felt like it didn’t quite stand on its own.”

Facebook’s Reactions bear a close resemblance to several established Unicode characters, with some minor tweaks here and there. The team attempted to exploit the subtle visual cues that differentiate facial-based emoji through a variety of stylistic choices. In early tests, the design team heightened the color saturation and bolded the outlines. They made eyes more pronounced or used unorthodox forms altogether, replacing circular faces with stars. Finally, they arrived at a major insight: In order to reflect a reaction, their emoji actually needed to react.

The final six reactions, animated.

When a user thumbs over each of the emoji, they animate like tiny GIFs. For "Wow," the yellow face tilts upwards, its mouth agape. For "Haha," a squinty-eyed emoji tilts its head back in a fit of laughter. “When we started animating them, everyone instantly got it,” says Zhuo. Other visual details like eyebrows make the faces more expressive, especially at smaller sizes. “Angry, in particular, becomes a lot more alive with eyebrows,” Teehan adds. Keltner says he suggested that Facebook incorporate voice into the reactions to clarify the signal even further. “One of the things I’ve been pitching to Facebook is to put in little vocalizations,” he says, adding that the voice is one of the richest carriers of emotional information. That, too, was an engineering problem. "Maybe in the future," he says.

Making Room for Reactions

For Zhuo and her team, the next major challenge was figuring out how to shoehorn five new interactions into an interface that had previously afforded just three actions: like, comment, and share. The team toyed with various layouts. The most obvious option was to present all six emoji beneath every post, with a number signaling how many people had selected each. But that solution “began to break down even in internal testing,” says Teehan; posts with a lot of reactions became too cluttered with feedback. So they tried the opposite, grouping all of the reactions into a single counter. But this watered down the core goal of increasing emotive expression. “When we aggregate these posts into a single word like reaction we’re taking away a lot of beauty of the sentiment,” Teehan says.

They found a middle road: Under every post, the three most commonly selected reactions will appear beside the reactions of your algorithmically determined best friends. You can see the full reaction-breakdown by clicking through. Zhuo explains, “As somebody who is just scanning newsfeed at a glance you could understand... the general sentiment of how people are reacting to the story.”

Facebook has never been afraid to alter its design, and those changes have not always been well received. But Reactions is almost certainly a good move for the company. Looking past Facebook's altruistic narrative about an expanded emotional palette, it's really just a bid to increase engagement, which will ultimately make your news feed (and ads) even more personalized. Still, it's well done. If all goes according to plan, the new reactions will integrate seamlessly into the existing platform. In two weeks' time, we'll probably forget they weren't there from the start. As Evans rightly puts it: “This is an obvious step—to be honest, the only surprise I have is that it’s taken them til now to do it."