You can see the new buttons by either holding down the like button (if you’re on your phone or tablet) or hovering over it (if you’re on your desktop). Tap the emoji reaction you want, and the icon for it will appear beneath the post, just as the like icon does.

Facebook will tell you that the new reactions are all about giving users new ways to communicate and express themselves. No doubt that’s part of it. Users have long complained that like doesn’t feel appropriate in a lot of circumstances, such as when a friend’s loved one has died or an acquaintance posts a political screed that you find interesting but also troubling.

But, like almost everything Facebook does, there is a double purpose at work here—and that second purpose involves data. Specifically, Facebook is now going to be able to collect, and profit from, a whole lot more of it.

Facebook. Mary Altaffer/Associated Press

In a January Slate cover story, I looked behind the scenes at how Facebook’s news feed algorithm works—how it decides what you see at the top of your feed every time you log in—and why the company keeps tweaking it.

In short, Facebook has come to believe that the key to its long-term success lies in gathering ever more and ever richer data on how its users react to the posts they see in their feed.

The company can use that data to personalize each user’s feed to her liking, so that it never becomes so stale, repetitive, or overwhelming that she’s tempted to look elsewhere for her daily fix of updates from friends. Much of the same data goes into the software Facebook uses to decide which ads its users see in their feeds.

The like button, from the beginning, has been a key source of that data. When you like something in your feed, you’re implicitly telling Facebook to show you more of it. But if the like button is your only option, you’re not really telling it much about how you really feel about a given post.

In contrast, giving users six reaction options means that Facebook can start to gather much more nuanced data on how users are reacting to any given post. It can begin to differentiate between posts that users are enjoying, posts they find fascinating, posts that make them happy, and posts that make them sad.

Facebook says that it isn’t using the data from new reactions in that way—yet. But that will soon change, according to a blog post from Facebook’s Krug:

Initially, just as we do when someone likes a post, if someone uses a Reaction, we will infer they want to see more of that type of post. In the beginning, it won’t matter if someone likes, “wows” or “sads” a post — we will initially use any Reaction similar to a Like to infer that you want to see more of that type of content. Over time we hope to learn how the different Reactions should be weighted differently by News Feed to do a better job of showing everyone the stories they most want to see.