Put it at the exact beat where the mishap happens, after It Was At This Moment He Knew sets up the fall, then follow it with Fail Sound Meme to underline the flop before the scene moves on.
关于此声音
This is a very short drum and cymbal impact, under half a second long, with a bright crash and a falling whistle-bong underneath. It feels sudden and silly, like a pratfall landing in a single beat. The clip comes from Baggage Buster, a Goofy cartoon from 1941.