The rumors are true: Facebook has indeed been working on a Snapchat competitor called Slingshot, and true to its ephemeral nature, it showed up ever so briefly on the App Store today before it was taken down. Prior to that though, we managed to glean enough information from the app description to get a few hints as to how it works. Similar to Snapchat, you can send photos and videos to friends, and once they view them, those messages will disappear. You're even able to add captions and scribblings on them just like Snapchat. But the key differentiator between Slingshot and other ephemeral messaging apps is that before your friends can see your missives, they must reciprocate and "sling" something back. After receiving your message, they can either tap to react to it or swipe it to remove it for good.