This clip comes from Team Four Star's Hellsing Ultimate Abridged, a fan-made parody of the Hellsing Ultimate anime, and is labelled as coming from its second episode. Team Four Star built a large online following by redubbing anime with sharp, comedic dialogue, and short reaction lines from those episodes became easy to lift for other videos. The single-word delivery works on its own because listeners recognise the tone even without the original scene, which is why it continues to appear in memes, streams and edits as a quick way to signal disbelief.