Put it just after the confusing reveal, then follow it with Bruh Meme for a second reaction, or with Fail Sound Meme when the confusion turns into a clear mistake. For a slower build, open with It Was At This Moment He Knew before the reveal, then let this clip answer it.
About this sound
A very short spoken exclamation, just over a second long, in which a voice blurts out 'What da fa!' in a startled, rising tone. The delivery is abrupt and incredulous, as if something impossible to believe has just been heard. It feels funny and bewildering, perfect for a moment of pure confusion, with the sheer disbelief making it land even harder.