The anime Nani sound effect is a short shocked Japanese exclamation of disbelief, used for surprise reveals, plot twists and funny reaction moments in memes.
This is a brief, sharply delivered Nani clip, the Japanese word for what, spoken with sudden disbelief and a rising, almost incredulous tone that lands in just over a second. The voice is loud and startled rather than calm, so the single word feels like a double take caught on audio. It works because listeners instantly recognise the exaggerated anime-style shock, even without seeing the scene, and that instant recognition turns a quiet moment into a punchline. Played over a reveal, it makes the surprise feel bigger, sillier and more dramatic, as if the character on screen has just had their whole world interrupted.
Nani is the Japanese word for what, and in anime dialogue it is often shouted when a character is stunned, confused or confronted by something unbelievable. Clips of that startled delivery spread online as a reaction sound, passed between meme pages, anime edits and short-form videos where a single word could carry the whole joke. It remains popular because it needs no translation for many viewers, who recognise the tone of disbelief immediately, and because its brevity makes it easy to place over reveals, fails and unexpected twists without slowing the edit down.