Place it at the reveal, just as the trick becomes clear, then follow it with a shocked sound to sell the reaction and an Oh No No No Laugh to close the bit. That order gives the prank a clear payoff, a visible reaction and a quick finish without stretching the joke too far.
About this sound
This is a short prank clip, lasting about five seconds, built around a sudden gag meant to catch someone off guard. It lands with a playful, mischievous energy that makes a set-up feel complete and a reaction feel bigger. The humour comes from the timing of the surprise rather than any long build-up, so it works best as a quick payoff after a trick has been set in motion.