Place it right after the strange reveal, then follow it with a SpongeBob Fail sound for the failed outcome and a Dun Dun Dun sound when the twist gets serious.
About this sound
This 2.4-second clip is a male Sim voice giving a short, rising eh, the kind of sound made when a plan falls apart in front of you. It feels puzzled and slightly awkward, like catching yourself mid-thought with no good reply. It comes from The Sims, where Sims use their own playful language instead of real words.