Just the one repetitive sound, the high pitched note played over and over. Iunno, maybe I just don't see it. You know it wasn't till a few years ago that I understood the joke 'seven ate nine' so... yeah, my brain works differently.
For some reason that music reminds me of Kefka. Kefka was one weird ass crazy clown that ended up being one of the most badass villains in video game history.
It's Levan Polkka as Tenboro said. The original song is even in the video description for Your Face. The only difference is Fluttershy is just doing the song itself and not the Savo Finnish scatting that's in the original. Here's the instrumental of Miku's Levan Polkka and Fluttershy's Your Face. Play them both and you should get the comparison.