Duolingo is a language learning app built around short lessons, streaks and its green owl mascot Duo. Duo became a meme figure online for the app's persistent reminders, summed up in jokes like Spanish or vanish about what happens if you skip a lesson. Clips of Duo praising a correct answer spread on soundboards and in fan edits as the positive side of that joke, a reward after the pressure. The short correct line is now reused far beyond lessons as a general sound for getting something right.