Duolingo launched in 2011 as a free language learning app built around short lessons, instant feedback and daily streaks tracked with its owl mascot Duo. Getting answers right triggers a positive ding sound effect, and longer streaks feel like an achievement worth sharing. As lessons were screen recorded for TikTok, YouTube Shorts and classroom memes, the correct answer sound escaped the app and became shorthand for learning wins and smug success. Its link to streak culture, where users protect an unbroken run of days, keeps it relevant.