On a Wednesday almost one year ago, Facebook product designers Joey Flynn and Brandon Walkin decided to work from home. They discussed how frustrating it is that modern smartphones aren't designed with texting in mind, since that’s what we’re doing most of the time. It's impossible to multitask while texting with friends — who are, more often than not, faceless entities organized by row inside a texting app.

"We had always talked about how apps with messaging components inside them are always the best," Flynn says. "We thought that it would be awesome if every app could have a messaging component." Or, what if your friends could somehow be one tap away as you found directions, looked up a restaurant, or responded to an email? Nearly two days later, "Chat Heads" started coming into focus — icons of your friends that stay with you no matter what app you're using. Tapping a friend pops your conversation with them into the foreground. With a flick, the conversation zips into the background.

They spent hours mocking up the idea, putting faces inside circles, and then squares, and then rounded rectangles. They decided on circles, a recent trend for avatar pictures, then added white borders, and then scrapped the borders. They stacked faces vertically, and then horizontally, and tooled with rubber-banding animations inside Apple’s Quartz Composer software. "It was one long night, one crazy idea, and that's how it started," says Flynn.